Airworthiness Directives; de Havilland, Inc. DHC-6 Series Airplanes

SUMMARY: This amendment adopts a new airworthiness directive (AD) that

applies to de Havilland DHC-6 series airplanes. This action requires

revising the Airplane Flight Manual (AFM) to provide the flight crew

with recognition cues for, and procedures for exiting from, severe

icing conditions, and to limit or prohibit the use of various flight

control devices. This amendment is prompted by results of a review of

the requirements for certification of the airplane in icing conditions,

new information on the icing environment, and icing data provided

currently to the flight crews. The actions specified by this AD are

intended to minimize the potential hazards associated with operating

the airplane in freezing rain or freezing drizzle conditions by

providing more clearly defined procedures and limitations associated

with such conditions.

EFFECTIVE DATE: June 11, 1996.

ADDRESSES: Information that relates to this AD may be examined at the

Federal Aviation Administration (FAA), Central Region, Office of the

Assistant Chief Counsel, Attention: Rules Docket 96-CE-01-AD, Room

1558, 601 E. 12th Street, Kansas City, Missouri 64106.

FOR FURTHER INFORMATION CONTACT: Mr. John Dow, Aerospace Engineer, FAA,

Small Airplane Directorate, 1201 Walnut, suite 900, Kansas City,

Missouri 64106; telephone (816) 426-6934; facsimile (816) 426-2169.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal

Aviation Regulations (14 CFR part 39) to include an AD that would apply

to de Havilland DHC-6 series airplanes was published in the Federal

Register on January 25, 1996 (61 FR 2175). The action proposed to

require revising the Airplane Flight Manual (AFM) to specify procedures

that would prohibit flight in freezing rain or freezing drizzle

conditions (as determined by certain visual cues), limit or prohibit

the use of various flight control devices, and provide the flight crew

with recognition cues for, and procedures for exiting from, severe

icing conditions.

Disposition of Comments

Interested persons have been afforded an opportunity to participate

in the making of this amendment. Due consideration has been given to

the comments received.

In addition to the proposed rule described previously, in January

1996, the FAA issued 17 other similar proposals that address the

subject unsafe condition on various airplane models (see below for a

listing of all 18 proposed rules). These 17 proposals also were

published in the Federal Register on January 25, 1996. This final rule

contains the FAA's responses to all public comments received for each

of these proposed rules.

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Docket No. Manufacturer/airplane model Federal Register citation

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96-CE-01-AD de Havilland DHC-6 Series............... 61 FR 2175

96-CE-02-AD EMBRAER EMB-110P1/EMB-110P2............. 61 FR 2183

96-CE-03-AD Beech 99/200/1900 Series................ 61 FR 2180

96-CE-04-AD Dornier 228 Series...................... 61 FR 2172

96-CE-05-AD Cessna 208/208B......................... 61 FR 2178

96-CE-06-AD Fairchild Aircraft SA226/SA227 Series... 61 FR 2189

96-CE-07-AD Jetstream 3101/3201..................... 61 FR 2186

96-NM-13-AD Jetstream BAe ATP....................... 61 FR 2144

96-NM-14-AD Jetstream 4101.......................... 61 FR 2142

96-NM-15-AD British Aerospace HS 748 Series......... 61 FR 2139

96-NM-16-AD Saab SF340A/SAAB 340B/SAAB 2000 Series.. 61 FR 2169

96-NM-17-AD CASA C-212/CN-235 Series................ 61 FR 2166

96-NM-18-AD Dornier 328-100 Series.................. 61 FR 2157

96-NM-19-AD EMBRAER EMB-120 Series.................. 61 FR 2163

96-NM-20-AD de Havilland DHC-7/DHC-8 Series......... 61 FR 2154

96-NM-21-AD Fokker F27 Mark 100/200/300/400/500/600/ 61 FR 2160

700/050 Series.

96-NM-22-AD Short Brothers SD3-30/SD3-60/SD3-SHERPA 61 FR 2151

Series.

95-NM-146-AD Aerospatiale ATR-42/ATR-72 Series....... 61 FR 2147

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Comment 1. Support for the Proposals

Numerous commenters support the FAA's intent to minimize the

potential hazards associated with operating airplanes of any type

design in severe icing conditions. One commenter states that the

limitation prohibiting the use of flaps while enroute and during

holding in icing conditions will be a positive contribution to safety.

Additionally, several commenters support the requirement of the

proposed AD for Aerospatiale airplanes for installation of modified

deicing boots on the outer leading edges of the wings. One of these

commenters states that the incorporation of AFM procedures, in addition

to installation of the modified boots, provide a substantial margin of

safety for the Aerospatiale fleet.

Comment 2. Requests Concerning References to ``Freezing Rain/Freezing

Drizzle''

Raytheon requests that references to a class of meteorological

conditions in the limitations described as ``freezing rain or freezing

drizzle'' should be removed from the proposed rules. Raytheon contends

that instructions for the flight crew should be restricted to hazardous

conditions that are defined by the accumulation of ice. The commenter

states that the term ``severe icing'' has a specific meaning as defined

in the Aeronautical Information Manual: ``The rate of accumulation is

such that the icing/anti-icing equipment fails to reduce or control the

hazard. Immediate diversion is necessary.'' The commenter states that,

although freezing rain or freezing drizzle may involve drops larger

than those specified in Appendix C of part 25 (``Airworthiness

Standards: Transport Category Airplanes'') of the Federal Aviation

Regulations (14 CFR part 25), flight into those conditions does not

always result in accumulation

[[Page 20617]]

of ice beyond the capability of the aircraft nor is severe icing always

the result of freezing rain or freezing drizzle. Raytheon concludes

that the limitation specified in paragraph (a)(1) of the proposals

which reads, ``Flight in meteorological conditions described as

freezing rain or freezing drizzle, as determined by the following

visual cues, is prohibited,'' is an inference or conclusion that does

not follow from the premises.

The European Regional Airlines (ERA) Association states that the

proposals define visual cues to be used to identify ``freezing rain''

and ``freezing drizzle,'' but these criteria are inconsistent with the

criteria defined by the International Civil Aviation Organization

(ICAO) and used by weather observers in aviation meteorological support

services. The FAA infers from this remark that ERA requests the use of

ICAO terminology associated with the visual cues.

The FAA concurs partially. The FAA concurs that most of the

references to ``freezing rain/freezing drizzle'' can be removed from

the final rules. The FAA has revised the final rules to replace certain

references to freezing rain and freezing drizzle with the words

``severe icing.'' The FAA finds that since the visual cues contained in

paragraph (a)(1) of these final rules indicate that icing conditions

have exceeded the limits of the ice protection equipment, the use of

the terminology ``severe icing'' is appropriate. As stated by one

commenter, ``severe icing'' is terminology used to describe icing

conditions that exceed the capabilities of the ice protection

equipment. The terminology ``severe icing'' is commonly used and

understood within the aviation community. Additionally, there should be

no confusion over the use of this term in the final rules because the

AFM revisions required by these AD's define the terminology ``severe

icing'' by specifying the visual cues that indicate when the

capabilities of the ice protection equipment have been exceeded.

However, the FAA would consider a request for approval of an

alternative method of compliance to use terminology other than ``severe

icing'' in an AFM, in accordance with the provisions of these AD's,

provided that adequate justification is presented to support such a

request.

Any inconsistencies that may exist between the criteria used by

weather specialists to define ``severe icing'' and the criteria stated

in these final rules are not relevant for these AD's because these AD's

do not require the flight crew to take any action based on information

provided by a weather observer. For these AD's, the flight crew must

only take action if certain visual cues are present on the airplane.

The FAA has determined that reference to freezing rain and freezing

drizzle should not be removed from the text of the ``Caution'' that

appears in paragraph (a)(2) of the proposals. [Note: The ``Caution''

appears as the ``Warning'' in paragraph (a)(1) of the final rules. An

explanation of this change is contained in the disposition of Comment

49 of these final rules.] Reference to freezing rain and freezing

drizzle in that portion of text is made simply to provide a description

of conditions that may result in ice build-up that exceeds the

capabilities of the ice protection system.

Comment 3. Request for Review of ``Severe Icing'' Terminology

One commenter, the Civil Aviation Authority (CAA), which is the

airworthiness authority for the United Kingdom, requests that use of

the terminology ``severe icing'' be reviewed. The CAA does not believe

it is appropriate that this terminology becomes accepted for

supercooled large droplet (SLD) conditions. The CAA indicates that a

common interpretation for ``severe icing'' is that beyond the limit

specified in Appendix C of part 25 of the Federal Aviation Regulations

(14 CFR part 25), which is at or just over the capability of the ice

protection system.

The FAA has reviewed the use of the terminology ``severe icing'' as

related to SLD. The FAA finds that ice resulting from SLD conditions

may not always meet the criterion specified in the common

interpretation of ``severe icing,'' as described by the commenter. The

FAA notes that while SLD conditions may result in the formation of

severe icing, severe icing also may accrue in conditions such as liquid

water content, temperature, or extent of cloud, when those conditions

exceed the limits specified in Appendix C of part 25 of the Federal

Aviation Regulations (14 CFR part 25). As explained previously, most

references to freezing rain and freezing drizzle have been replaced

with the terminology ``severe icing.'' Additionally, the AFM's for the

affected airplanes include a definition of severe icing.

Comment 4. Request To Withdraw the Proposals: Significant Economic

Impact on Operating Community

A number of commenters request that the proposals be withdrawn

because the effect of these proposed AD's will produce a significant

economic impact on the operating community. The commenters indicate

that many flights would need to be canceled in order to make all

reasonable efforts to avoid encounters with freezing rain/freezing

drizzle conditions--i.e., when these conditions are forecast, airplanes

will be prohibited from flight into those conditions. One commenter

remarks that, based on the actual weather in January 1996, nearly 75

percent of its scheduled flights would have been canceled due to

forecast or actual freezing rain or freezing drizzle conditions if the

AD's had been in effect. The commenters do not believe that the FAA has

considered the economic factors affected by the proposed actions, such

as the number of flights lost per day, crew costs, passenger

compensation, misconnected baggage, etc.

If the FAA does not withdraw the proposals, one commenter states

that the prohibition of flight in freezing rain or freezing drizzle, as

specified in paragraph (a)(1) of the proposals, should be revised. The

commenter suggests the following: ``The aircraft should be immediately

flown clear of icing conditions if ice is seen forming on the upper

surface of the wing behind the leading edge deice boots.'' The

commenter believes that the current wording in the proposals would

cause flight crews to cancel or delay departure not only when freezing

rain or freezing drizzle exists, but also when those conditions are

forecast.

The FAA concurs partially. The FAA finds that some misunderstanding

exists among the commenters concerning the intent of these AD's. Many

of the commenters believe that the AD's will prevent affected airplanes

from flight in forecast freezing rain and freezing drizzle. This is not

the case. The FAA agrees that certain language contained in the AD's

must be clarified to reflect its intent. The FAA has evaluated the

wording proposed by one of the commenters and agrees with it in

principal. However, the FAA has determined that the first limitation in

paragraph (a)(1) of the final rules must be revised in order to

accommodate visual cues other than that specified by the commenter, to

incorporate terminology familiar to the flight crew, and to emphasize

that these AD's address only in-flight icing encounters. Additionally,

in order to ensure that appropriate coordination with Air Traffic

Control is accomplished, the FAA has revised the instruction following

the visual cues in paragraph (a)(1), and has moved that instruction to

the end of the first limitation in paragraph (a)(1) of the final rules.

The entire limitation reads as follows: ``During flight, severe icing

conditions

[[Page 20618]]

that exceed those for which the airplane is certificated shall be

determined by the following visual cues. If one or more of these visual

cues exists, immediately request priority handling from Air Traffic

Control to facilitate a route or an altitude change to exit the icing

conditions.'' (Operators should note that, in the final rule for

Aerospatiale airplanes, only one visual cue is specified. That cue

involves ice on the side window of the airplane.)

Several commenters question certain issues related to dispatch of

the airplane in severe icing conditions. One commenter states that the

procedures specified in the proposed AD's fail to address the

conditions that would prohibit takeoff in freezing rain and freezing

drizzle. The commenter believes the visual cues provided in the

proposals would only appear on an airplane during flight. Thus,

allowable conditions for takeoff during times of forecast freezing rain

or freezing drizzle are left to the individual operator's

interpretation. Another commenter believes that the FAA has not

established a basis for prohibiting flight in all reported freezing

drizzle. The commenter contends that takeoff in freezing rain should

always be prevented, but takeoff in freezing drizzle should be possible

after applying appropriate deicing or anti-icing treatments. One

commenter requests that the FAA clarify how the procedures for exiting

freezing rain/freezing drizzle conditions would apply to takeoff and

landing. The commenter states that landing during those conditions

might, in many cases, be the most expeditious method of avoiding a

hazardous condition. Another commenter suggests that the AFM for

Aerospatiale airplanes should be revised to reflect standard dispatch

rules; however, the commenter provides no justification for this

request.

The FAA concurs that visual cues that would prohibit takeoff in

freezing rain or freezing drizzle were not provided because the FAA's

intent is that these AD's address only in-flight icing encounters.

These AD's do not affect any existing regulations or FAA-approved

operating procedures related to takeoff, dispatch, or release of an

airplane in icing conditions. These AD's only prohibit remaining in

icing conditions when certain visual cues are present on the airplane;

these AD's do not prohibit flight into forecast or reported freezing

drizzle. Operators must comply with existing rules that require an

airplane to be free of ice prior to takeoff. Further, the FAA finds no

need to revise the AFM for Aerospatiale airplanes to reflect standard

dispatch rules. The FAA also considers that landing the airplane when

freezing rain/freezing drizzle conditions are encountered would, in

many cases, be the most expeditious method of exiting the conditions.

Such landing would be in compliance with the limitation that requires

the flight crew to exit the severe icing conditions.

Two commenters indicate that the first note that appears in

paragraph (a)(1) of the proposed rules could be interpreted to mean

that if freezing rain or freezing drizzle is forecast anywhere along

the route of flight, the airplane could not be dispatched. One of the

commenters concludes that forecasting methodologies are inadequate and

would need to be improved. The other commenter suggests that the FAA

remove the word ``purely'' from the note. The same commenter requests

that the FAA clarify that the airplane may be dispatched if the

forecast may indicate freezing rain/freezing drizzle conditions.

Another commenter indicates that the wording of the same note is

unclear as to how the FAA defines a ``purely'' inadvertent encounter.

The commenter states that examples of such purely inadvertent

encounters would be helpful.

One commenter asks the following questions in regard to the same

note:

--What are ``reasonable efforts?''

--What does ``immediately exit'' mean? Are the procedures for

immediately exiting listed in the Air Traffic Controller's Handbook or

the Airman's Information Manual? Can a pilot operating the airplane in

a holding pattern decide on his/her own to immediately descend below

the freezing level without regard to other traffic?

One commenter states that the note should be placed in the Normal

Procedures Section of the AFM, rather than in the Limitations Section.

The commenter provides no justification for this request.

The FAA concurs that clarification of this note is necessary. The

FAA originally included the note in the AD's to clarify the intent of

the rules. Since the first instruction and the limitation that follows

have been revised in these final rules, the FAA finds that inclusion of

the clarifying note is no longer necessary. In order to avoid any

possible misinterpretation of the intent of the limitation on flight in

freezing rain or freezing drizzle, the FAA has removed the first note

that appeared in paragraph (a)(1) of the proposals. These AD's do not

prohibit flight into forecast or reported freezing rain or freezing

drizzle. This means that the aircraft is not prohibited from takeoff,

dispatch, or release simply because the forecast may indicate freezing

rain or freezing drizzle, but is prohibited from continued flight in

severe icing conditions.

Comment 5. Request To Withdraw the Proposals: No Unsafe Condition Has

Been Established

Several commenters request that the proposals be withdrawn because

no unsafe condition has been established with respect to airplane

handling characteristics in severe icing conditions. One commenter

states that the preamble of the proposals does not provide data that

establish an unsafe condition; the preamble only indicates that there

are inadequate data to represent all possible conditions. Another

commenter remarks that the FAA's dismissal of the significance of the

test results with the specious comment, ``such airplanes could develop

ice shapes other than those tested,'' is wholly speculative, and is an

invalid basis on which to issue an AD under the provisions of part 39

(``Airworthiness Directives'') of the Federal Aviation Regulations (14

CFR part 39).

The FAA does not concur that these AD's should be withdrawn. As

stated in the preamble to the proposals, the FAA has not required that

airplanes be shown to be capable of operating safely in icing

conditions outside the icing certification envelope specified in

Appendix C of part 25 of the Federal Aviation Regulations (14 CFR part

25). This means that any time an airplane is flown in icing conditions

for which it is not certificated, there is a potential for an unsafe

condition to exist or develop and the flight crew must take steps to

exit those conditions expeditiously. Further, the FAA has determined

that flight crews are not currently provided with adequate information

necessary to determine when an airplane is operating in icing

conditions for which it is not certificated or what action to take when

such conditions are encountered. The absence of this information

presents an unsafe condition because without that information, a pilot

may remain in icing conditions for which the airplane has not been

proven to be safe. These AD's correct the unsafe condition by requiring

AFM revisions that provide the flight crews with visual cues to

determine when icing conditions have been encountered for which the

airplane is not certificated, and by providing procedures to safely

exit those conditions.

Additionally, in the preamble to the proposed rules, the FAA

discussed the investigation of roll control anomalies to explain that

this investigation was not a

[[Page 20619]]

complete certification program. The testing was designed to examine

only the roll handling characteristics of the airplane in certain

droplets the size of freezing drizzle. The testing was not a

certification test to approve the airplane for flight into freezing

drizzle. The results of the tests were not used to determine if these

final rules were required, but rather to determine if design changes

were needed to prevent a catastrophic roll upset. The roll control

testing and the AD's must be viewed as two unrelated actions.

Comment 6. Request To Withdraw the Proposals: Unsafe Condition Is

Outside Certification Limits

One commenter states that the proposed AD's should be withdrawn

because the issuance of AD's to address the problems of icing

encounters outside of the limits for which the airplane is certificated

is a completely inappropriate application of part 39 of the Federal

Aviation Regulations (14 CFR part 39). Another commenter contends that

since the Aerospatiale aircraft passed all present certification

testing, what transpired beyond the limits of certification should not

be held against that aircraft.

The FAA does not concur that the AD's should be withdrawn on the

basis that the unsafe condition is outside the icing certification

envelope. Flight in icing conditions that are outside the icing

certification envelope occurs during the normal service life of an

airplane. Apart from the visual cues provided in these final rules,

there is no existing method provided to the flight crews to identify

when the airplane is in a condition that exceeds the icing

certification envelope. The appropriate vehicle for providing this

method of identification is through issuance of an AD. The FAA

acknowledges that the Aerospatiale airplane has been shown to comply

with existing certification rules; however, no airplane is certificated

for flight in icing conditions outside of Appendix C of part 25 of the

Federal Aviation Regulations (14 CFR part 25).

Comment 7. Request To Withdraw the Proposals: Proposals Unfairly

Discriminate Against Turbopropeller-Powered Aircraft

Several commenters state that the proposed AD's should be withdrawn

because the AD's unfairly discriminate against turbopropeller-powered

aircraft. The commenters contend that by issuing these proposed rules,

the FAA is creating a public perception that turbopropeller-powered

aircraft are less safe than other aircraft.

Numerous commenters oppose the statement contained in the preamble

of the proposals which indicates that since turbopropeller-powered

airplanes are more likely to operate at low altitudes and to make more

frequent landings, they are more likely to encounter icing conditions

that are outside the icing envelope. One commenter states that the mere

fact that turbopropeller-powered airplanes make more frequent landings

is irrelevant for the following reasons:

--Every flight encounters the same atmospheric conditions after takeoff

and prior to landing, whether the airplane is powered by a

turbopropeller or turbojet engine;

--There are numerous airplanes powered by turbojet engines that operate

on segments equal in duration to those operated by many turbopropeller-

powered aircraft; numerous airplanes powered by turbojet engines make

just as frequent landings; and

--Even if turbopropeller-powered aircraft do make more frequent

landings, there is no negative inference to be drawn from that fact;

more opportunities are available to ensure that ice has not formed on

the aircraft if the aircraft lands more frequently.

One commenter states that the altitudes where SLD conditions exist

are the same altitudes at which jets would encounter those conditions

during the departure and arrival phases of flight. Flight in SLD

conditions that would have a negative effect on a turbopropeller-

powered airplane would have the same effect on a jet, since both are

certificated under the same rules with regard to flight into adverse

weather, and both fly at about the same speeds during the departure and

arrival phases of flight. Additionally, another commenter adds that no

airplane, whether it is powered by a turbopropeller, turbojet, or

turbofan engine, is certificated for operation in SLD conditions.

Another commenter indicates that icing encounters take place at

altitudes below the cruising altitudes of most turbopropeller-powered

aircraft used in scheduled service; this also occurs on airplanes

powered by turbojet engines. Icing encounters occur during takeoff,

climb, descent, holding, and landing phases of flight on both types of

aircraft. The commenter adds that operating the airplane in a holding

pattern for a prolonged period in severe icing conditions is hazardous

for both turbojet and turbopropeller-powered aircraft. The commenter

explains that, although the exposure time per flight hour of a long-

haul jet aircraft is less, the exposure on a per flight basis is

exactly the same. The commenter states that, like landing gear life

limits, the proper measure of exposure to freezing rain/freezing

drizzle should be the number of flights, not the number of flight

hours.

Another commenter, Saab, states that Saab Model SAAB 2000 series

airplanes have a unique power-to-weight ratio, which makes it

comparable with airplanes of the same size and, in some relevant areas

such as climb performance and single engine ceiling, even far superior.

Operators of those airplanes can operate the aircraft over-the-weather

at flight level (FL) 310. This means that these Saab airplanes operate

on jet profiles and, therefore, are not exposed to the icing conditions

that are outside the icing envelope any more than the airplanes that

are excluded from the proposals.

The FAA does not concur that the proposals should be withdrawn. The

FAA does not intend to imply through issuance of these AD's that

turbopropeller-powered airplanes are less safe than airplanes having

other types of propulsion systems. As stated in the preamble of the

proposals, the FAA addressed certain airplanes as a higher priority for

two reasons:

--Turbopropeller-powered airplanes are more likely to operate at low

altitudes and to make more frequent landings; therefore, they are more

likely to encounter icing conditions that are outside the icing

envelope specified in Appendix C of part 25 of the Federal Aviation

Regulations (14 CFR part 25); and

--The flight crew of an airplane having an unpowered roll control

system must rely solely on physical strength to counteract roll control

anomalies, whereas a roll control anomaly that occurs on an airplane

having a powered roll control system need not be offset directly by the

flight crew.

Since the issuance of the proposed rules, the FAA has reconsidered

this reasoning. The FAA acknowledges that simply because an airplane is

turbopropeller-powered and has a particular flight profile, that

airplane should not be addressed as a higher priority. However, this

does not diminish the significance of the necessity of the flight crew

of an airplane having an unpowered roll control system to rely on

physical strength to counteract roll control anomalies. The subject

airplanes all have pneumatic deicing boots and unpowered aileron

controls, which have been common denominators in the accident and

incident history

[[Page 20620]]

concerning flight in icing conditions and, in particular, during

conditions when SLD was believed to be present. Therefore, airplanes

having those design features are of immediate concern to the FAA and

were addressed as a higher priority. Additionally, these AD's primarily

address airplanes used in regularly scheduled passenger service in the

United States.

The FAA finds that the comment indicating that more frequent

landings provides more opportunity to verify that ice has not formed is

irrelevant. It also could be said that more frequent landings gives

more opportunity for ice to form. The FAA agrees with the statement

that holding for prolonged periods in severe icing conditions is

hazardous for all aircraft types. The FAA is considering initiating an

assessment of the need to prohibit all aircraft from continued flight

in severe icing conditions as defined in these AD's.

Although Transport Canada Aviation does not request that the

proposed AD's be withdrawn, the commenter indicates that roll control

anomalies could exist for all aircraft whether they have powered or

unpowered roll control systems. Transport Canada Aviation adds that

some jet-powered aircraft have unpowered ailerons.

The FAA concurs that roll anomalies could exist for all aircraft

whether they have powered or unpowered roll control systems. However,

these AD's address airplanes having both deicing boots and unpowered

aileron controls. The FAA acknowledges that other airplanes that have

powered ailerons may be subject to roll problems in severe icing

conditions due to loss of lift. However, the FAA is not aware of a

mechanism that would allow ice to produce an uncommanded control

deflection on airplanes having powered flight control systems. In

addition, airplanes having powered roll control systems do not have

direct feedback of aerodynamic forces to the pilot. However, the FAA is

considering initiating an assessment of the need to apply similar

limitations to other aircraft types.

Comment 8. Request To Withdraw the Proposals: Affected Airplanes Are

Not Same Type Design as Accident Airplane

Several commenters contend that the proposals should be withdrawn

because the FAA has not established clearly that the airplanes

addressed in the proposed rules have the same type design as the

Aerospatiale Model ATR-72 series airplane that was involved in an

accident in October 1994 that occurred in severe icing conditions.

One commenter questions the words ``same type design,'' and asks if

those words refer to high wing, low wing, T-tail, or aircraft of

another type design.

Three commenters provide justification in support of a request that

certain airplanes be exempt from these AD's:

de Havilland Model DHC-7 and DHC-8 series airplanes: De

Havilland states that the airplanes it manufactures share a

conservative aerodynamic design philosophy that yields exceptional low-

speed handling qualities and demonstrated benign handling qualities in

icing conditions. De Havilland adds that two-thirds of the roll control

authority of these airplanes is provided by hydraulically powered roll

spoilers. A second commenter adds that increased testing has been

conducted on these airplanes.

Fokker F27 Mark 100, 200, 300, 400, 500, 600, 700, and 050

series airplanes: Fokker states that the leading edge boots on Fokker

Model F27 series airplanes and Model F27 Mark 050 series airplanes

extend to a chord wise position, 12.5 percent wing chord, which

precludes all but the very largest droplets impinging on the

unprotected surfaces. Fokker adds that since the accident airplane has

unshielded horn balances and the affected Fokker airplanes do not have

these unshielded horn balances, Fokker airplanes will not experience

roll upset problems. Fokker indicates that aerodynamically balancing

the control surfaces by means of unshielded horn balances was not

applied because of the bad service experience of the Vickers Viking

aircraft in 1946.

Beech Model 200 and 200C airplanes: Raytheon states that

these particular airplane models are not normally considered to be

commuter aircraft, and that issuance of an AD would be contrary to the

stated purpose of the proposals because most of these airplanes are

used in non-revenue service. Raytheon states that these airplanes are

all low wing aircraft. Aerospatiale Model ATR-72 series airplanes (the

accident airplane) is 50 percent larger and carries over twice the

number of passengers as these Beech aircraft. For these reasons, as

well as other differences in the geometry of the airplanes (i.e.,

relative aileron span), Raytheon states that the supposition of an

icing hazard in these aircraft is purely speculative.

The FAA does not concur that any of the addressed airplanes should

be exempt from these AD's. The FAA has examined the accident and

incident history in icing conditions and, in particular, those events

believed to involve SLD conditions. Results of this examination

revealed that the type design characteristics that appear to be common

in these events are pneumatic deicing boots and unpowered aileron

controls. Airplanes having those type design characteristics appear to

be more susceptible to control problems in severe icing conditions. In

response to Fokker's remark that its airplanes will not experience roll

control problems since those airplanes do not have unshielded horn

balances, the FAA has determined that horn balances on the accident

airplane were not the source of the uncommanded aileron motion. Design

similarities of the wing, tail, or ailerons do not appear to be a

common denominator among airplanes involved in accidents or incidents

where SLD conditions may have been present.

Saab asks for removal of the sentence that reads, ``Since an unsafe

condition has been identified that is likely to exist or develop on

other airplanes of the same type design * * *.'' Saab states that this

sentence implies that Saab Model SF340A and SAAB 340B series airplanes

have a problem and that this problem is ``likely to develop on other

airplanes of the same type design.'' Yet, there have been no reported

problems on those airplanes, which are not of the same type design as

all other turbopropeller-powered airplanes. Transport Canada Aviation

does not request that the proposals be withdrawn; however, the

commenter requests that the FAA revise the same phrase discussed by

Saab. Transport Canada Aviation requests that the phrase be reworded as

follows: ``Since an unsafe condition has been identified where aircraft

icing certification is not adequate to address the conditions that are

outside of Appendix C of FAR part 25 * * *.''

The FAA does not concur with Saab's request. The FAA acknowledges

that there have been no reported problems involving severe icing

conditions on Saab airplanes. However, Saab Model SF340A and SAAB 340B

series airplanes have pneumatic deicing boots and unpowered aileron

controls, which have been determined to be the common denominators

among the airplanes involved in accidents and incidents in severe icing

conditions. Therefore, the FAA has determined that when severe icing

conditions are encountered on these Saab airplanes, those conditions

must be exited.

Although the FAA has no technical objection to the revised wording

proposed by Transport Canada Aviation, this sentence does not reappear

in the final rules. Therefore, no change to the final rule is

necessary.

[[Page 20621]]

Comment 9. Request for Explanation of the Applicability of the AD's

One commenter requests an explanation of the methodology used by

the FAA to determine that AD's should not be issued for Cessna and

Piper multi-engine aircraft. The commenter also asks if an AD similar

to the proposed rules exists for Boeing Model 737 series airplanes. The

commenter indicates that Model 737 series airplanes have demonstrated

abnormal and unexplained roll tendencies.

The FAA provides the following clarification for this commenter. No

AD's have been issued for Piper airplanes or Boeing Model 737 series

airplanes. However, as reflected in the table above, the FAA has issued

an AD for Cessna Model 208 and 208B airplanes.

Most of the aircraft affected by these final rules are used

primarily in regularly scheduled passenger service in the United

States. However, there are some airplanes affected by the final rules

that are not used in regularly scheduled passenger service. Two of

these are Cessna Model 208 and 208B airplanes. Those airplanes were

included in the final rules because of their accident and incident

history in icing conditions. The FAA is considering an assessment of

the need to prohibit all aircraft from continued flight in severe icing

conditions.

Comment 10. Request To Withdraw the Proposals: Service Experience of

Affected Airplanes Is Satisfactory

Several commenters indicate that the FAA should withdraw the

proposed AD's in light of the satisfactory service experience of the

airplanes addressed in the proposals. The commenters believe that the

FAA is singling out turbopropeller-powered aircraft without any regard

for the operational record of those aircraft.

Several commenters provide justification in support of this

request:

One commenter states that de Havilland airplanes have been

successfully operated for over 30 years without one instance of roll

upset or flight control problems.

De Havilland indicates that de Havilland Model DHC-8

series airplanes have been in service for 11 years and have accumulated

6 million flights and 5 million flight hours without any incidents due

to icing.

De Havilland adds that de Havilland Model DHC-7 series

airplanes have been in service for 18 years and have accumulated 3.7

million flights and 2.7 million flight hours without any incidents due

to icing.

Another commenter has not experienced any icing related

upsets or control irregularities in its fleet of de Havilland Model

DHC-8 series airplanes and Beech Model 1900 series airplanes.

One commenter operates 21 Beech Model 1900D airplanes, 32

EMBRAER Model EMB-120 series airplanes, and 41 Aerospatiale Model ATR-

42 and ATR-72 series airplanes; none of these airplanes have

experienced any icing incidents this season.

One commenter indicates that airplanes produced by Beech,

EMBRAER, and Jetstream Aircraft Limited (JAL) have no record of

uncommanded roll due to asymmetrical build-up of ice on surfaces beyond

the deicing boots.

One commenter notes that it has not experienced any

unusual icing characteristics on its fleet of EMBRAER Model EMB-120

series airplanes and Aerospatiale Model ATR-72 series airplanes.

Fairchild notes that in over 26 years and 15,000,000

flight hours in passenger service, there has never been a reported

incident where the controllability of Fairchild Aircraft SA226 and

SA227 series airplanes were in jeopardy as a result of any icing

encounters (including SLD icing encounters).

The Luftfartsverket (LFV), which is the airworthiness

authority for Sweden, states that no ice build-up behind the wing boots

has ever been reported on Saab Model SF340A, SAAB 340B, or SAAB 2000

series airplanes. Additionally, the leading edge on these airplanes can

be inspected easily during flight.

Saab remarks that no roll anomaly problems in icing

conditions have occurred during the extensive service experience of

Saab Model SF340A and SAAB 340B series airplanes.

The FAA does not concur that the AD's should be withdrawn. The fact

that an airplane has a perfect safety record in icing does not negate

the fact that no airplane has been certificated for flight into SLD.

The FAA has determined that a need exists to provide the flight crew

with useful safety-related information regarding the limitations of the

airplane concerning flight in severe icing conditions. The purpose of

issuing these final rules is to provide the flight crew with such

information.

One commenter, Transport Canada Aviation, requests that the

proposals apply only to those airplanes that have a demonstrated

history of in-service problems as a priority. The commenter states that

the hazards relating to operation in icing conditions exist for all

types of aircraft. (The commenter does not request that the proposed

rules be withdrawn.)

The FAA does not concur with this request. As explained previously,

the FAA has issued AD's for airplanes having pneumatic deicing boots

and unpowered aileron controls as a priority. Airplanes having these

design features are of immediate concern to the FAA because these

features have been common denominators in the accident and incident

history concerning flight in icing conditions and, in particular,

during conditions when SLD was believed to be present. The FAA is

considering the need for rulemaking to impose similar limitations on

other aircraft.

Comment 11. Request To Withdraw the Proposals: Extensive Testing

Revealed No Icing Problems

Several commenters request that the proposals be withdrawn because

extensive testing revealed no icing problems on many different

turbopropeller-powered airplanes, even though those tests likely

exceeded any icing certification tests ever performed on other civil

aircraft types, including large jet-powered transport category

airplanes. Fokker states that Fokker Model F27 series airplanes do not

demonstrate unacceptable roll control characteristics in severe icing

conditions; however, Fokker submits no data to substantiate this

statement.

The FAA does not concur. The FAA finds that successful completion

of the roll upset evaluation is not a valid reason for withdrawing the

AD's. On the contrary, if the evaluation had demonstrated anomalies,

the FAA may have concluded that action beyond that required by these

AD's was necessary to address the demonstrated unsafe condition. The

testing was designed to examine only the roll handling characteristics

of the airplane in certain droplets the size of freezing drizzle to

determine if any design changes are necessary to prevent catastrophic

control surface deflection. The testing was not a certification test to

approve the airplane for flight into freezing drizzle since many of the

components and their functions were not tested (e.g., pitch control,

engine and propeller, performance, stall warning, windshield, air data

sensors and fuel system vents). Further, freezing rain was not tested.

Satisfactory demonstration of those tests does not remove the FAA's

responsibility to provide a safe operating environment for the

passengers and crew.

JAL comments that its airplanes are not subject to the addressed

unsafe condition, and that the FAA had

[[Page 20622]]

concurred with this contention. JAL states that the FAA agreed that, by

the controllability evaluation process, all Jetstream aircraft types

had been demonstrated to be not susceptible to roll control anomalies

in freezing rain or freezing drizzle conditions.

The FAA does not concur with JAL's position concerning its

airplanes. All Jetstream airplanes affected by these AD's successfully

completed the roll upset evaluation. However, as stated previously, no

airplanes were tested in freezing rain conditions. The roll upset

evaluation only addressed conditions that were believed to have existed

during an accident involving a transport category airplane that

occurred in October 1994. Therefore, since no airplane has been tested

in all freezing rain and freezing drizzle conditions, no airplane has

been demonstrated to be safe for continued flight in these conditions.

Comment 12. Request To Withdraw the Proposals: Publish Advisory

Materials and Require Training

Several commenters request that, in lieu of issuing the proposed

rules, the FAA publish appropriate advisory materials and require

training for recognition, avoidance, and exit from severe icing

encounters as part of the required severe weather training for pilots

and dispatchers. Two commenters suggest that the FAA include such

requirements in the operating rules specified in part 121

(``Certification and Operations: Domestic, Flag, and Supplemental Air

Carriers and Commercial Operators of Large Aircraft'') of the Federal

Aviation Regulations (14 CFR part 121). Another commenter indicates

that, since jets and piston-engine aircraft also could develop ice

shapes other than those tested, training should not be provided only to

pilots of turbopropeller-powered airplanes, but to pilots of all

aircraft. Some commenters also suggest that the FAA has successfully

addressed other issues through increased awareness and training

requirements, rather than by issuing AD's against every airplane type

design to require revising the Limitations Section of the AFM. The

commenters cite windshear, ground deicing, and clear air turbulence as

examples of such issues. The commenters contend that, except where

configuration changes are needed, such as in the case of windshear

detection devices, improved awareness and training programs--not AD's--

have been highly effective in achieving needed safety improvements.

The FAA does not concur. The FAA considers that substituting

advisory material and mandatory training for issuance of an AD is not

appropriate, nor would this adequately address the unsafe condition.

The FAA fully supports the development of advisory materials and

training. Part 121 (``Certification and Operations: Domestic, Flag, and

Supplemental Air Carriers and Commercial Operators of Large Aircraft'')

and part 135 (``Air Taxi Operators and Commercial Operators'') of the

Federal Aviation Regulations (14 CFR parts 121 and 135) require that

appropriate training concerning limitations such as those contained in

these AD's be incorporated into air carriers' training programs.

However, the FAA's position is that the development and use of such

advisory materials and training alone are not adequate to address the

subject unsafe condition. Currently, the AFM's specify that the

affected airplanes are certificated for flight in icing conditions;

however, the AFM's do not specify a method of determining whether the

certification limits for those conditions have been exceeded.

Consequently, the FAA finds that these AFM's must be revised to provide

limitations for flight in icing conditions and to provide the flight

crew with a method of determining when those limitations have been

exceeded.

The FAA does not concur that amending part 121 of the Federal

Aviation Regulations (14 CFR part 121) in lieu of issuing these AD's is

appropriate. The FAA's position is that the appropriate place to inform

the flight crew of the limitations of the airplane is in the AFM. The

appropriate vehicle for mandating such AFM revisions is through

issuance of an AD. In addition, an AD will ensure that the

incorporation of such AFM revisions is not left to each operator's

individual discretion and that flight crews receive pertinent

information. The FAA may consider an assessment of the need to provide

training to pilots of all aircraft types for flight in severe icing

conditions.

The commenters reference windshear as an example of an issue that

was handled successfully without issuance of an AD to revise the AFM's.

In this case, the AFM's for all airplanes having an onboard windshear

system were revised to provide the flight crew with procedures for

responding when the system gives an alert. Although no AD was issued to

mandate these AFM revisions, without revising the AFM, operators could

not comply with the section of part 121 of the Federal Aviation

Regulations (14 CFR part 121) that requires installation of the

windshear detection devices. In conclusion, although AFM revisions were

not required by an AD, AFM changes were mandated indirectly by a new

part 121 regulation.

The commenters also reference ground deicing. Part 91 (``General

Operating and Flight Rules'') of the Federal Aviation Regulations (14

CFR part 91) prohibits takeoff of an airplane unless the airframe is

clear of ice; therefore, there is no need to provide additional

limitations concerning the amount of ice that would be acceptable for

takeoff. However, in the case of severe icing conditions addressed by

these final rules, the AFM's currently allow flight in icing, but the

AFM does not define when the limits of the certificated icing operation

envelope have been exceeded.

Concerning the issue of clear air turbulence, issuance of an AD was

not required because an airspeed limitation associated with turbulent

air penetration was already in the AFM's. Therefore, in this case, the

issue was addressed in the AFM as well as through awareness and

training.

Comment 13. Request To Withdraw the Proposals: Incorporate Operational

Issues Into a Training Curriculum

Two commenters request that the proposals be withdrawn because the

proposed AD's address an operational issue that should be incorporated

into an operator's training curriculum. One commenter states that

pilots must be made aware of the hazards of icing and that extended

operation of an airplane in any icing encounter that results in

significant airframe accretion of ice is unacceptable.

The FAA does not concur that the AD's should be withdrawn based on

the commenters' request. The FAA acknowledges that these AD's address

an operational issue. When the requirements of these AD's are

accomplished and the AFM limitations are revised, this material will be

incorporated necessarily, as explained previously, into the training

curriculum for the flight crews and dispatchers, if applicable, in the

operator's approved training program. In this manner, pilots and

dispatchers, if applicable, will be informed of the hazards of icing

and that continued operation of an airplane in certain icing conditions

is prohibited.

Comment 14. Request To Withdraw the Proposals: Require Training for Air

Traffic Controllers and Weather Specialists

Two commenters request that the FAA implement additional policy to

require training for air traffic controllers and weather specialists in

the

[[Page 20623]]

recognition, avoidance, and procedures to exit severe icing conditions.

The FAA does not concur that these AD's should be withdrawn.

However, the FAA acknowledges that implementation of these AD's may

necessitate additional training beyond that which is already required

for air traffic controllers and weather specialists. The FAA may

consider the need to provide training concerning recognition,

avoidance, and procedures for exiting severe icing conditions. However,

the intent of these AD's is to provide the flight crew with recognition

cues for, and procedures for exiting from, severe icing conditions. The

appropriate vehicle for requiring that such information be included in

the AFM's is through issuance of an AD.

Comment 15. Request To Withdraw the Proposals: Add a Caution to the AFM

One commenter requests that, in lieu of issuing the proposed AD's,

a ``Caution'' should be added to the AFM to inform pilots to exit icing

conditions if ice was observed to be forming aft of the protected

surfaces of the wings. The commenter states that information regarding

the use of flaps and the autopilot in icing conditions could also be

incorporated into the AFM. The commenter does not indicate which

section of the AFM should include this material.

The FAA does not concur. The FAA finds that the requirement to exit

severe icing conditions and information concerning use of the autopilot

during flight in those conditions must be included in the Limitations

Section of the AFM. Additionally, information concerning use of the

flaps during those conditions should be included in the Procedures

Section of the AFM. The appropriate vehicle for requiring these changes

to the AFM is through issuance of an AD.

Comment 16. Request To Withdraw the Proposals: Require Alternative AFM

Limitation

One commenter requests that, in lieu of an AD, the FAA require an

alternative AFM limitation that reads as follows: ``This aircraft is

certified for flight into icing conditions as specified by Appendix C

of Part 25. Actual icing encountered may be greater than Appendix C

requirements.''

The FAA does not concur. The suggested limitation does not provide

guidance as to how a pilot can identify and safely exit icing

conditions that have exceeded those specified in the icing envelope in

Appendix C of part 25 of the Federal Aviation Regulations (14 CFR part

25). These AD's are intended to provide the flight crew with visual

cues which indicate that icing conditions have exceeded the

capabilities of the ice protection equipment, and with procedures to

safely exit those conditions. No change to the AD's is necessary.

Comment 17. Request To Withdraw the Proposals: AFM Revisions Already

Are Required

One commenter requests that the proposals be withdrawn because

section 121.133 (``Manual Requirements: `Preparation' '') of the

Federal Aviation Regulations (14 CFR 121.133) already requires that

operators incorporate revisions into the AFM's; therefore, issuance of

the proposed AD's is unnecessary.

The FAA does not concur. Section 121.133 of the Federal Aviation

Regulations (14 CFR 121.133) does not specifically require that AFM's

be updated to current revisions. Section 121.141 (``Airplane or

Rotorcraft Flight Manual'') of the Federal Aviation Regulations (14 CFR

121.141) requires that the current AFM be carried on the aircraft, but

does not require incorporation of the most current revisions.

Additionally, the commenter does not address the need to change the

AFM's for airplanes that operate under parts 135 (``Air Taxi Operators

and Commercial Operators'') and 91 (``General Operating and Flight

Rules'') of the Federal Aviation Regulations (14 CFR parts 135 and 91).

The appropriate vehicle for ensuring that the Limitations Section of

the AFM's is changed is through issuance of an AD.

Comment 18. Request To Withdraw the Proposals: Use Existing AFM

Revisions

The General Aviation Manufacturers Association (GAMA), on behalf of

its members, states that some of the affected manufacturers have

prepared FAA-approved revisions for the AFM's for their products. GAMA

indicates that those revisions incorporate specific information

regarding cues for recognizing severe icing conditions and procedures

for exiting such conditions, if encountered. Therefore, if the proposed

AD's are adopted, the requirements of the AD's would supersede the

information operators have already incorporated into the AFM's with

less appropriate information that is not type design specific.

One commenter, JAL, requests that certain existing AFM revisions

for the affected Jetstream airplanes be cited in the proposed AD's for

those airplanes in lieu of the content of the proposed AD's. (However,

JAL does not request that the proposals be withdrawn for this

particular reason.) JAL indicates that the existing AFM revisions have

already been FAA-approved.

The FAA does not concur with the commenters' requests. The FAA

acknowledges that the AFM revisions required by these final rules will

supersede previously approved AFM revisions. However, the FAA is

unaware of any AFM that addresses all of the provisions specified in

these final rules, nor of any AFM that contains specific visual cues

that the FAA has not included in the final rules. Even if AFM material

currently exists that does contain all of the provisions of the final

rules, the FAA finds that issuance of an AD would still be necessary to

mandate the provisions of the AFM revisions. However, the FAA would

consider a request for approval of an alternative method of compliance,

in accordance with the provisions of this AD, for those operators

having AFM's that already contain all of the provisions of the final

rules.

Another commenter requests that the FAA withdraw the proposal that

applies to Fairchild Model SA226 and SA227 series airplanes. The

commenter states that the AFM for those airplanes currently contains

visual cues to aid the flight crew in recognition of weather conditions

conducive to SLD. This AFM also provides procedures for avoidance of

such conditions. The commenter adds that these AFM procedures result in

additional operating limitations on the aircraft with regard to severe

weather conditions. The commenter believes these AFM procedures address

all current FAA requirements.

The FAA does not concur that the AFM for Fairchild Model SA226 and

SA227 series airplanes addresses all of the proposed requirements of

the proposed rule. For example, the Limitations section of the AFM for

those airplanes does not require the flight crew to exit severe icing

conditions. For this reason, the FAA does not consider the AFM for

Fairchild Model SA226 and SA227 series airplanes to be equivalent to

the information specified in these AD's.

Comment 19. Request To Withdraw the Proposals: Develop Rulemaking To

Address Airplane Certification Outside of Appendix C

Three commenters suggest that instead of arbitrarily prohibiting

operation of the airplane, the FAA should undertake a well-designed

research program and, if warranted, devise a rulemaking plan for

certification of airplanes outside of Appendix C of part 25 of the

Federal

[[Page 20624]]

Aviation Regulations (14 CFR part 25). One commenter also suggests

possible retroactive implementation of a new Appendix C.

The FAA does not concur because of the length of time that would be

required to implement the commenters' suggestion. The FAA finds that

action is required prior to the commencement of the next icing season

to prohibit the continued flight of airplanes in icing conditions that

have been shown to be unsafe and for which the airplanes have not been

certificated. However, the FAA is currently considering initiating an

assessment of the need to revise Appendix C and the possibility of its

retroactive implementation.

Transport Canada Aviation states that the FAA has determined that

there may be a problem with the certification requirements for icing on

de Havilland Model DHC-6, DHC-7, and DHC-8 series airplanes, but not

the specific approval or design features of those airplanes. However,

the commenter does not specifically request that the proposals be

withdrawn.

The FAA does not concur with the commenter's statement. The FAA has

only determined that no adequate means exists for the flight crew to

determine when the icing certification limits have been exceeded. The

purpose of these AD's is to provide more clearly defined procedures and

limitations associated with severe icing conditions. This does not

imply that the certification requirements for icing are inadequate.

Comment 20. Request To Withdraw the Proposals: Issue a ``General AD''

for All Airplane Types

One commenter requests that a ``general AD'' be issued to prohibit

all airplane types from inadvertent flight into hazardous SLD

conditions. Another commenter adds that if encounters with freezing

rain/freezing drizzle conditions must be reported to Air Traffic

Control, such reporting also should apply to flight crews of all

airplane types.

The FAA does not concur with the commenter's request. For the

reasons discussed earlier in the preamble of this AD, the FAA has

determined that airplanes having pneumatic deicing boots and unpowered

aileron controls are of immediate concern and have been addressed as a

higher priority. The FAA finds that action is required prior to the

commencement of the next icing season to prohibit the operation of

these airplanes in icing conditions that have been shown to be unsafe

and for which the airplanes have not been certificated. However, the

FAA is currently considering initiating an assessment of the potential

adverse effects of SLD on all airplane types.

Comment 21. Request To Withdraw the Proposals: Establish a Detailed

Reporting System

One commenter requests that the FAA establish a detailed reporting

system for inadvertent encounters with severe SLD. The commenter

envisions a system that would provide a database for better

identification of controllability issues and visual indications related

to these encounters.

The FAA does not concur with the commenter's request. The FAA has

been advised that the Regional Airline Association (RAA) has already

established an ``Unusual Icing Reporting Program'' for the purpose

described by the commenter; therefore, establishing another reporting

program would duplicate this benefit.

Comment 22. Request To Withdraw the Proposals: Revise the Master

Minimum Equipment List (MMEL)

Two commenters request that, instead of addressing an MMEL item in

an AD [i.e., the icing detection lights referenced in paragraph (a)(1)

of the proposals], the FAA should require that the MMEL be revised. A

third commenter adds that the decision to change the MMEL should be

made by FAA Operations Inspectors based on local conditions. One

commenter states that the prohibition of dispatch with any inoperative

ice detection lights would preclude any efforts by an operator to

enhance safety by installing a second set of bulbs. The commenter adds

that under this proposed rule, this type of action would be penalized

by simply doubling the chances of a burned out bulb grounding the

aircraft. In practice, if one were to add a fully redundant set of

bulbs, it would enhance safety by allowing the equivalent of the

current illumination level even with a bulb burned out.

The FAA does not concur with these requests. FAA Operations

Inspectors are not authorized to make MMEL revisions. The FAA has

determined that it is prudent to address the icing detection lights in

these final rules to ensure uniform and immediate application of the

requirements of the AD's. Concerning the example provided by one of the

commenters, if an operator chooses to add a fully redundant set of

bulbs, that operator should request approval of an alternative method

of compliance in accordance with the provisions of this final rule.

Although Transport Canada Aviation does not request that the

proposals be withdrawn, it requests a revision to the requirement that

all icing detection lights must be operative. For de Havilland Model

DHC-7 and DHC-8 series airplanes, the commenter requests that the

requirement be changed to mandate that at least one outboard and one

inboard inspection light be operative prior to flight into known or

forecast icing conditions at night. Since the MMEL contains a provision

that a suitable lamp/light of adequate capacity be available, this is

considered acceptable in conjunction with other indications of freezing

rain or freezing drizzle. Similarly, for de Havilland DHC-6 series

airplanes, the requirement should be revised to require a suitable

lamp/light for dispatch at night with one wing inspection light

inoperative.

The FAA does not concur. The FAA has determined that the

justification provided by the commenter is not adequate to enable the

FAA to determine if the proposed changes are acceptable. During severe

icing conditions, the flight crew's workload may be high, and there may

be no opportunity to use the portable lamp/light, which, in itself, may

create disorientation in the cockpit due to adverse reflections from

the glass. The FAA's intent in having all inspection lights be

operative at night is to provide the flight crew the best possible

visibility of the airframe. However, the FAA would consider a request

for approval of an alternative method of compliance, in accordance with

the provisions of these AD's, provided that adequate justification is

presented to support such a request.

Comment 23. Request To Withdraw the Proposals: Certify Airplanes for

Flight in Conditions Outside Appendix C

One commenter implies that the airplanes affected by the proposed

rules must be rectified to a level beyond the present certification

requirements for flight in icing.

The FAA does not concur. The final rules do not require

certification of the airplane beyond the current certification

requirements for flight in icing specified in Appendix C. These AD's

simply provide the flight crew with visual cues which indicate that

icing conditions have exceeded the capabilities of the ice protection

equipment, and with procedures to safely exit those conditions.

One commenter requests that the proposal for de Havilland DHC-6

series airplanes be withdrawn because this airplane model is type

certificated in Canada, which is a country with a higher standard than

the United States for operating in icing conditions.

[[Page 20625]]

The FAA does not concur. This commenter did not submit data to the

FAA to substantiate that the airplane has been shown to be safe for

flight outside the icing certification envelope specified in Appendix

C. Additionally, the FAA is unaware of any foreign civil aviation

authority having certification requirements for icing conditions that

are outside of the icing certification envelope used in the United

States.

Comment 24. Request To Withdraw the Proposals: Proposals Prohibit

Takeoff or Approach in ``Light Freezing Drizzle'' Conditions

One commenter requests the proposals be withdrawn because the

proposed limitation would prohibit takeoff or approach when ``light

freezing drizzle'' conditions that are caused by light precipitation

falling through a thin layer of cold surface air below warmer air above

are reported on the surface. The commenter maintains that with

accomplishment of the appropriate ground deicing precautions prior to

takeoff, no hazard to the operation of the airplane is posed.

The FAA does not concur that the AD's should be withdrawn for this

reason. These AD's do not affect any existing regulations or FAA-

approved operating procedures related to takeoff, dispatch, or release

of an airplane in icing conditions, nor do these AD's prohibit

operation in specific meteorological conditions. These AD's only

prohibit remaining in icing conditions when certain visual cues are

present on the airplane. Operators must comply with existing rules that

require an airplane to be free of ice prior to takeoff. Therefore,

takeoff in ``light freezing drizzle'' would only be prohibited by

existing regulations or FAA-approved operating procedures, not by these

AD's. As explained previously, the FAA considers that landing the

airplane when freezing rain/freezing drizzle conditions are encountered

would, in many cases, be the most expeditious method of exiting the

conditions. Such landing would be in compliance with the limitation

that requires the flight crew to exit the severe icing conditions.

Comment 25. Request To Withdraw the Proposals: Proposals Leave

Unanswered Questions

One commenter contends that the proposals leave unanswered

questions. The commenter alleges that without the answers to those

questions, affected parties are deprived of the ability to provide

informed comments and, thereby, are ``denied their rights under the

Administrative Procedures Act (APA) to comment on the proposed rules.''

Specifically, the commenter asks:

--What is unusual icing?

--Does the pilot, Air Traffic Control, dispatch, or the FAA determine

when the conditions exist?

--What is splatter effect?

--Where are the operating instructions incorporated--in the AFM,

training manuals, or some other document?

The FAA infers from the commenter's remarks that the commenter requests

the proposed AD's be withdrawn because informed comments could not be

provided.

The FAA does not concur that the AD's should be withdrawn on this

basis. The FAA does not agree that the public has been deprived of the

ability to provide informed comments, as required by the APA. In

general, the APA requires that notice of the terms or substance of a

proposed rule be published in the Federal Register. The purpose of this

requirement is to ensure that federal agencies thoroughly consider all

information and opinions submitted by the public before any

requirements are imposed. Notice is intended to improve both the

quality of the regulations and their acceptability to the public. The

FAA finds that none of the questions raised by the commenter identify

areas in which the commenter has not been provided a reasonable

opportunity to comment. The fact that the commenter raises questions

suggests that the commenter considers a need for further clarification.

Even if the commenter is correct in that these questions require

clarification, that fact in itself is a comment that can be addressed

properly by simply clarifying terms. The fact that clarification is

necessary does not mean that the public has been denied reasonable

opportunity to comment.

In response to the commenter's questions, the FAA provides the

following clarification. The term ``unusual icing'' did not appear in

the proposed rules. However, the phrase ``unusually extensive ice'' is

referenced in paragraph (a)(1) of the final rules. [This reference

appears in paragraph (a)(2) of the final rule for Aerospatiale

airplanes.] ``Unusually extensive ice'' accrued on the airframe in

areas not normally observed to collect ice is a visual cue that is

subject to interpretation by the flight crew; therefore, a specific

definition of ``unusually extensive ice'' cannot be provided.

These AD's address changes to AFM limitations, which pertain to the

pilot since the pilot is responsible to look for the visual cues

defined in the AD's. Therefore, the pilot determines when severe icing

conditions exist.

The terminology ``splatter effect'' did not appear in the proposed

rules. The FAA infers from the commenter's question that the commenter

is referencing terminology used in paragraph (a)(2) of the proposed

AD's. ``Droplets that splash or splatter on impact at temperatures

below +5 degrees Celsius OAT'' is a visual cue that was included in the

proposed AD's as a method of identifying severe icing conditions.

Concerning incorporation of operating instructions, these final

rules specify that the AFM's be revised. The AD's do not specify that

any other manuals or documents be revised. However, information that is

included in the AFM as a limitation is necessarily included in the

training program.

Comment 26. Request To Clarify Scope of Icing Conditions Addressed

Transport Canada Aviation suggests that the proposals, which

address only freezing rain/freezing drizzle conditions, are not

adequate to cover all hazards related to operation of aircraft in icing

conditions. The commenter makes no specific request.

The FAA concurs that these AD's do not address all icing related

hazards. The FAA's intent is to minimize the potential hazards

associated with operating the airplane in severe icing conditions by

providing the flight crews with more clearly defined procedures and

limitations associated with such conditions. However, no change to the

final rules is necessary.

Comment 27. Request To Expand the Applicability of the AD's

One commenter, the CAA, suggests that the ``coverage'' of the

proposals should be stated clearly. The CAA believes that a restriction

to those operations in ``regularly scheduled passenger service'' is not

warranted for a safety issue as it does not cover cargo, charter, or

private operations. The commenter does not specify which airplane

models should be addressed. The FAA infers from the commenter's remarks

that it requests that the proposed AD's be applicable to other airplane

models that are used in cargo, charter, or private operations that may

have been excluded from the applicability of these AD's.

The FAA does not concur that the applicability of these AD's should

be expanded to include additional airplane models used primarily in

cargo, charter, or private operation. The FAA is currently considering

the need for

[[Page 20626]]

additional rulemaking to address other airplane models having pneumatic

deicing boots and unpowered aileron controls that are used in these

types of service that were not addressed by these AD's. Additionally,

the applicability of these final rules indicates that the AD's apply to

``all'' of the airplane models identified, certificated in any

category. This means that the AD's apply to all of the affected

airplanes, regardless of how those airplanes are operated (including

passenger service, cargo, charter, or private operation).

Comment 28. Request for Design Changes to the Airplanes

One commenter requests that the FAA require design changes to the

airplanes, which, when accomplished, will allow elimination of the AFM

limitations. The commenter states that abnormal roll control anomalies

could be eliminated by design changes that prevent any ice shapes from

forming by using supplemental ice protection added to existing

pneumatic boots or other ice protection installations. The commenter

concludes that, given this added protection, restricting flight in

freezing drizzle could be reduced to allow exposure to these

atmospheric conditions for a reasonable time and would not require

immediately exiting these conditions when encountered as presently

stipulated.

The FAA does not concur that it should require design changes to

airplanes in these AD's. Currently, the FAA is unaware of any design

changes that would allow elimination or reduction of the AFM

limitations specified in these AD's. However, if such design changes

are developed, approved, and become available, the FAA would consider

additional rulemaking to require such changes. The FAA finds that even

if the ice protection system prevented the formation of ice shapes in

front of the ailerons when the airframe is exposed to certain freezing

drizzle conditions, other meteorological conditions still exist (e.g.,

freezing rain) for which the airplane would not be certificated.

Comment 29. Request for More Specific Visual Cues

One commenter requests that the FAA provide more specific visual

cues for identification of freezing rain or freezing drizzle

conditions. The commenter states that the generic visual cues provided

in the proposed AD's are not adequate for aircraft types that

frequently operate in and encounter SLD conditions. For example, ice

could be forming on the upper wing and not the lower wing; therefore,

looking at the lower wing would not be a reliable visual cue. Two

commenters suggest that specific visual cues be provided for each

airplane model. One of these commenters states that subjective cues may

be of limited benefit if the pilot's experience with icing is

inadequate. The other commenter adds that subjective visual cues will

result in varying interpretations (i.e., some unnecessary course

changes in altitudes or service interruptions caused by overly

conservative interpretations). Transport Canada Aviation does not

request more specific visual cues; but states that ``unusually

extensive ice,'' ``normally observed,'' and ``farther back than

normally observed'' are all variable terms that are largely dependent

on flight crew experience. The commenter contends that limitations and

procedures described using these terms will not be consistently

interpreted. In addition, Transport Canada Aviation states that ice on

the lower wing surface aft of the protected area, by itself, is

unlikely to cause a hazard. Moreover, the presence or absence of such

ice cannot be used as an indication of any hazardous accumulation on

the upper wing surface or on the horizontal stabilizer.

The FAA does not concur with the commenters' request to provide

more specific (or airplane-specific) visual cues. The FAA agrees with

the commenters' assertion that, under certain circumstances,

examination of the undersurface of a high wing may not be reliable. The

FAA also agrees that other cues, such as unusually extensive ice

accrued on the airframe in areas not normally observed to collect ice

and accumulation of ice on the propeller spinner farther aft then

normally observed, are subjective and that reliance on pilot judgment

and experience is necessary in such cases. Additionally, the FAA fully

supports the development and use of airplane-specific cues by operators

and manufacturers. Unfortunately, no commenter provided airplane-

specific cues during this comment period.

In summary, the FAA finds that the combined use of the generic cues

provided and the effect of the final rules in increasing the awareness

of pilots concerning the hazard of operating outside of the

certification icing envelope will provide an acceptable level of

safety. However, for those operators that elect to identify airplane-

specific visual cues, the FAA would consider a request for approval of

an alternative method of compliance, in accordance with the provisions

of this AD.

Transport Canada Aviation states that the term ``protected area''

may not be readily recognizable by the flight crew; for example, not

all of a deicing boot surface is ``protected area.'' [This terminology

appears in the second visual cue (in the proposals for airplanes other

than Aerospatiale airplanes) and in the autopilot limitation in

paragraph (a)(1) of the proposals. For Aerospatiale airplanes, this

terminology appears in the secondary indications in paragraph (a)(1) of

the proposal.] The FAA infers that the commenter requests that more

specific language than ``protected area'' be used.

The FAA does not concur that this terminology should be revised.

The FAA considers that a pilot understands that a portion of the

deicing boot would be considered to be unprotected. Therefore, no

additional clarification or definition of the term ``protected area''

is necessary.

Comment 30. Request To Reference Clear Icing Conditions and Clear

Component of Mixed Icing Conditions

One commenter also asks that all references to freezing rain and

freezing drizzle environments and visual cue identification reference

clear icing conditions and the clear component of mixed icing

conditions. According to the commenter, mixed icing conditions can

contain areas of freezing rain and/or freezing drizzle. The commenter

notes that mixed icing has taken on two different definitions within

the aviation community--the ``engineering'' definition (which is

defined in an FAA icing handbook) and the definition pilots use (which

includes areas of clear and rime ice). The commenter states that a

clear definition of these conditions is needed. The commenter adds that

only pilot reports can show that freezing rain/freezing drizzle exists

because forecasting of these conditions is inadequate. The commenter

indicates that while the Aerospatiale airplanes have side window cues

that will accurately identify freezing rain or freezing drizzle, pilots

of other airplanes without such a sophisticated cue may erroneously

report mixed icing.

The FAA does not concur. The FAA acknowledges that freezing rain

and freezing drizzle may be reported as clear/mixed icing conditions.

However, the flight crew must exit icing conditions that produce the

visual cues specified in the final rules. Exiting the icing conditions

is not dependent upon the terminology used to describe the conditions.

Therefore, the FAA has determined that it is not necessary to include

references to clear icing

[[Page 20627]]

conditions and the clear component of mixed icing conditions. In

addition, the FAA has determined that including a discussion in these

AD's of the phenomenon of mixed icing conditions as it relates to the

current state-of-the-art weather forecasting would be premature because

no clear definition of this phenomenon has been agreed upon among the

aviation community. The FAA is currently considering an assessment

during which various icing-related subjects, including mixed icing

conditions, would be addressed.

Comment 31. Request for Research and Use of Wing-Mounted Ice Detectors

One commenter requests that wing-mounted ice detectors, which

provide real-time icing severity information (or immediate feedback) to

flight crews, continue to be researched and used throughout the fleet.

The FAA infers from this commenter's request that the commenter asks

that installation of these ice detectors be mandated by the FAA.

While the FAA supports the development of such ice detectors, the

FAA does not concur that installation of these ice detectors should be

required. The specifications for automatic detectors having the

capabilities to differentiate among freezing rain, freezing drizzle,

and other icing conditions have not been determined. However, if such

ice detectors are developed, approved, and become available, the FAA

may consider further rulemaking action to require installation of such

equipment.

Comment 32. Request to Limit the Applicability of the AD's

One commenter requests that the applicability of the proposals be

limited to airplanes having NACA 430xx airfoils. The commenter asserts

that the unusual pressure peak on the NACA 430xx airfoils at 9 percent

chord caused the ice ridge to form at that point, which resulted in the

accident involving a Aerospatiale Model ATR-72 series airplane. The

commenter states that ``the accident was caused by the poorly designed,

unusual, and fortunately rarely used NACA 430xx airfoils used on this

airplane.''

The FAA does not concur with the commenter's request to limit the

applicability of the AD's. First, the National Transportation Safety

Board (NTSB) has not yet made an official finding of the probable cause

of the accident referenced by the commenter. Therefore, the FAA cannot

assume that airplanes having NACA 430xx airfoils are more susceptible

to the addressed unsafe condition than those airplanes that do not have

this type of airfoil. Second, the FAA has examined the data submitted

by the commenter, and disagrees with the commenter's assertion

concerning the formation of ice ridges. The formation of ice ridges

depends on many factors. Ice ridges have been observed to form in areas

where there is no pressure (commonly, ``suction'') peak. However, the

impingement location of large droplets is more relevant to the

development of ice ridges than the particular pressure distribution.

The commenter does not address the fact that, regardless of the type of

airfoil on an airplane, a substantial sharp edge protuberance in the

vicinity of the suction peak can have adverse consequences to the

aerodynamic performance of the airfoil. Regardless of the cause of

location of ice formations, prevention or removal of the ice is

certainly an acceptable remedy for such conditions, should those

conditions occur. For example, Aerospatiale extended the deicing boots

to prevent the formation of adverse ice ridges.

Comment 33. Request for Approval of Improved Deicing Equipment for

Aerospatiale Airplanes

ATR requests that paragraph (b) of the proposed rule for

Aerospatiale airplanes be revised to indicate that installation of any

improved version of deicing equipment that is approved by the FAA is

acceptable for compliance with the requirements of that paragraph. The

commenter provides no justification for its request.

The FAA does not concur with the commenter's request to revise the

AD. However, if an improved version of deicing equipment is developed,

approved, and available, the FAA would consider a request for approval

of an alternative method of compliance, in accordance with the

provisions of the AD.

Comment 34. Request for Re-Evaluation of Modified Deicing Boots on

Aerospatiale Airplanes

In response to the proposal for Aerospatiale airplanes, one

commenter requests that the new, enlarged deicing boots that are

required to be installed on these airplanes must be re-evaluated before

total confidence in the modified boots is warranted. The commenter

asserts that no test data exist to show that the modified boots will

preclude the problem of large droplets outside of Appendix C. The area

of exposure outside of Appendix C is essentially open-ended, and only

limited testing within a narrow range of droplet diameters was

conducted. Additionally, the test conditions that existed during the

tanker testing conducted at Edwards Air Force Base, which was intended

to be a ``before modification/after modification'' validation program,

were not identical. The commenter adds that no modification will ensure

that any airplane is safe while flying in icing conditions outside

those specified in Appendix C.

The FAA does not concur with the commenter's request for a re-

evaluation of the modified deicing boots. The modified deicing boots

for these airplanes were subjected to an extensive certification

program by both the FAA and the Direction Generale de l'Aviation Civile

(DGAC), which is the airworthiness authority for France. FAA approval

of the modified boots was based on engineering analyses, wind tunnel

testing, flight testing in natural icing conditions, and a validation

program involving a United States Air Force icing tanker. This testing

verified that the modified boots continue to perform the intended

function within the Appendix C icing envelope. In addition, the

extended deicing boots were shown to adequately protect the airplane

from the larger, supercooled water droplets that are believed to have

existed in the area at the time of the accident in October 1994.

It should be noted, however, that it is not intended that the

modified boots provide protection in all possible icing conditions,

including freezing rain/freezing drizzle. However, the FAA considers

that the combination of the enlarged deicing boots, the AFM operational

procedures and restrictions, and the visual cues which indicate entry

into freezing rain/freezing drizzle conditions provides for an enhanced

level of safety during inadvertent flight in these conditions.

Comment 35. Request for Formal Weather Forecasting System for Freezing

Rain/Freezing Drizzle

One commenter supports a requirement to establish a formal system

to provide forecasts of freezing rain/freezing drizzle conditions, as

proposed in paragraphs (b) and (c) of the original proposed rule for

Aerospatiale airplanes. [This proposed requirement was removed from the

subsequent supplemental notice of proposed rulemaking (NPRM) issued for

these airplanes in January 1996.] The commenter states that such a

requirement should remain in effect until forecasting tools are

developed or detection methods are established to prevent dispatch or

operations in conditions outside those specified in Appendix C. The

commenter states that

[[Page 20628]]

the efficacy of the deicing boots has not been shown completely nor

documented; therefore, avoidance of freezing rain/freezing drizzle is

paramount to safety of flight.

The FAA does not concur that such a requirement is necessary. The

FAA agrees that such a system would enhance the safety of flight

operations. However, there is no evidence that lack of a system with

such specialized features would lead to an unsafe condition. Forecasts

of freezing rain/freezing drizzle are a normal part of pre-flight

weather briefings. The FAA is aware, however, of serious limitations

for such a system to provide accurate and timely forecasts of these

conditions during flight in areas that are removed from weather

reporting stations. Quite often, the only indication of the existence

of severe icing conditions is from pilot reports or other direct

observations.

Research is underway currently in industry and the academic

community to address shortcomings in the forecasting of severe icing

conditions. The FAA may consider further rulemaking if advancements in

weather forecasting provide for a reliable method to predict the

occurrence of freezing rain/freezing drizzle conditions during flight

or in areas removed from direct observations.

Comment 36. Request To Approve Earlier Service Bulletin Revisions

One commenter to the proposed rule for Aerospatiale airplanes

requests that the proposed AD be revised to specify that earlier

revisions of service bulletins are acceptable for compliance with the

requirements of the proposed rule. The commenter makes this request so

as to eliminate the need to apply for approval of alternative methods

of compliance when accomplishing service bulletin revisions other than

those specified in the proposed rule.

The FAA does not concur that earlier revisions of the referenced

service bulletins should be cited in the final rule for Aerospatiale

airplanes. However, the FAA would consider a request for approval of an

alternative method of compliance, in accordance with the provisions of

the AD, provided that adequate justification is presented to support

such a request.

Additionally, the FAA has revised the revision levels specified for

certain service bulletins because those revision levels were omitted

inadvertently from paragraph (b) of the proposed rule for Aerospatiale

airplanes. That final rule has been revised to indicate that certain

modifications are to be accomplished in accordance with Revision 1 of

Aerospatiale Service Bulletins ATR42-57-0043, ATR72-57-1015, and ATR72-

57-1016. The correct date for Revision 1 of those service bulletins

(April 10, 1995) was specified in the proposal for the affected

airplanes.

Comment 37. Request To Revise Referenced Service Bulletins

One commenter to the proposal for Aerospatiale airplanes suggests

that service bulletin revisions should contain a statement indicating

that the revision has no effect on previously modified airplanes. The

commenter provides no justification for this request.

The FAA acknowledges that many service bulletins do contain the

suggested phrase as an aid to operators that may already have

accomplished an earlier service bulletin revision. In fact, if a

particular service bulletin is specified in an AD and that service

bulletin is revised, the FAA routinely determines whether the service

bulletin revision adequately addresses the unsafe condition specified

in the AD; if necessary, the FAA amends the AD to cite the later

service bulletin revision.

Comment 38. Request To Revise Visual Cue: Ice on Side Window

One commenter suggests revised wording for the first visual cue

specified in paragraph (a)(1) of the proposed rule for Aerospatiale

airplanes, as follows: ``Freezing rain and freezing drizzle are

characterized by ice covering all or a substantial part of the unheated

portion of either forward side window and/or water splashing or

streaming on the windshield or the side window when in freezing or near

freezing temperatures.'' The commenter states that the present wording

implies that ice will always appear on the side window; however, this

is not the case.

The FAA does not concur with the commenter's request. The

commenter's revised wording suggests that water splashing or streaming

on the windshield or the side window would be a primary cue used to

determine when severe icing conditions are present. The FAA does not

concur that water splashing or streaming on the windshield or the side

window would be a reliable cue in itself. However, this cue may be used

as a supplemental cue to the primary cue of ice accruing on the side

window. No change to the final rule for Aerospatiale airplanes is

necessary.

Comment 39. Request To Remove Visual Cue: Unusually Extensive Ice

Accretion

One commenter, Saab, requests that if the FAA does not withdraw the

proposed AD's, paragraph (a)(1) of the proposal for Saab SF340A and

SAAB 340B series airplanes should be revised. The commenter suggests

that the first visual cue that appears in that paragraph, which relates

to unusually extensive ice accretion, be removed from the proposal for

those airplanes. Saab indicates that critical ice is believed to be ice

that builds up beyond the protected surfaces on the wing. On Saab Model

SF340A and SAAB 340B series airplanes, the pilot has a good view of the

outer wing and the propeller spinner. Unusually extensive ice in other

areas may or may not be significant in determining whether freezing

rain or freezing drizzle is present; however, the primary visual cue

for these airplanes is ice on the spinner/outer wing.

In light of Saab's remarks, the FAA concurs that the visual cue

addressed by the commenter should be removed from the final rule for

Saab Model SF340A and SAAB 340B series airplanes. (That visual cue

remains in place for Saab Model SAAB 2000 series airplanes.) Paragraph

(a)(1) of that final rule has been revised accordingly.

A second commenter, Raytheon, requests that the same visual cue be

removed from the proposal for Beech airplanes. Raytheon indicates that

it does not believe that observation of this visual cue indicates that

the airplane has exceeded the Appendix C icing envelope with respect to

Beech airplanes. Therefore, the cue specified in the proposal would be

irrelevant in an AFM for these airplanes.

The FAA does not concur with Raytheon's request. The commenter has

not submitted data to warrant removal of the visual cue. No change to

the final rule for Beech airplanes has been made.

Comment 40. Request To Remove Visual Cue: Accumulation of Ice on Wing

Surfaces

JAL requests that the FAA remove the generic information contained

in the visual cue concerning accumulation of ice on the wing surfaces

from the proposals for Jetstream airplanes. JAL indicates that, for its

airplanes, the appropriate visual cue is the accretion of ice behind

the protected area of the wing upper surface (not the wing lower

surface).

The FAA concurs partially. The FAA does not agree that the visual

cue should be removed from the final rules for Jetstream airplanes.

However, the FAA finds that this particular visual cue should be

airplane-specific. Therefore, the FAA has customized paragraph (a)(1)

of the final rules for all affected airplanes to specify whether

accumulation of ice is observed on the

[[Page 20629]]

upper or lower surface of the wing, depending upon whether the airplane

is a high- or low-wing airplane. [Operators should note that, for

Aerospatiale airplanes, the cue was customized in paragraph (a)(2) of

the final rule.]

Comment 41. Request To Revise Visual Cue: Accumulation of Ice on

Propeller Spinner

One commenter requests that the FAA revise the visual cue

concerning accumulation of ice on the propeller spinner, as specified

in paragraph (a)(1) of the proposals. For consistency, the commenter

requests that the word ``back'' be replaced with ``aft.''

The FAA concurs with the commenter's request. The final rules have

been revised to change the visual cue to read as follows:

``Accumulation of ice on the propeller spinner farther aft than

normally observed.'' [Operators should note that, for Aerospatiale

airplanes, this change appears in paragraph (a)(2) of the final rule.]

Comment 42. Request To Remove Visual Cue: Accumulation of Ice on

Propeller Spinner

One commenter, JAL, requests that the FAA remove the visual cue

concerning accumulation of ice on the propeller spinner from the

proposals for Jetstream airplanes. JAL indicates that on Jetstream

Model ATP airplanes and Model 748 series airplanes, the propeller

spinner is not visible from the flight deck. On Jetstream Models 3101,

3201, and 4101 airplanes, the propeller spinner is visible from the

flight deck, but flight test experience indicates that there is no

unique correlation between the extent of spinner ice accretion and the

existence of freezing rain/freezing drizzle conditions.

The FAA concurs partially. The FAA concurs that since the propeller

spinner is not visible from the flight deck on Jetstream Model ATP

airplanes and Model 748 series airplanes, the visual cue can be removed

from paragraph (a)(1) of the final rules for these models. The FAA does

not concur that this visual cue should be removed from the AD's for

Jetstream Models 3101, 3201, and 4101 airplanes. The commenter did not

submit data to substantiate its assertion that flight test experience

indicates there is no unique correlation between the extent of spinner

ice accretion and the existence of freezing rain/freezing drizzle

conditions. Therefore, it is uncertain if the commenter's flight test

airplane was equipped with instrumentation that would allow the

detection and/or measurement of droplets outside the Appendix C

conditions, and if the airplane had flown into icing conditions

containing freezing rain or freezing drizzle.

Comment 43. Request To Remove Limitation to Immediately Exit Freezing

Rain/Freezing Drizzle

Saab requests that the FAA remove a sentence from paragraph (a)(1)

of the proposals that requires the pilot to immediately exit freezing

rain or freezing drizzle conditions by changing altitude or course.

This commenter points out that the first limitation contained in the

proposal for Saab airplanes (``Flight in meteorological conditions

described as freezing rain or freezing drizzle, as determined by the

following visual cues, is prohibited . . .'') already prohibits flight

in these conditions, and the pilot should respond accordingly. Raytheon

believes a conflict exists between using observations of ice accretion,

as required by paragraph (a)(1) of the proposed rules, and the

``determination'' of certain meteorological conditions.

The FAA concurs partially. The FAA does not agree that the sentence

discussed by Saab should be removed from paragraph (a)(1) of the final

rules. As explained previously, the first limitation in paragraph

(a)(1) of the final rules has been revised to read: ``During flight,

severe icing conditions that exceed those for which the airplane is

certificated shall be determined by the following visual cues. If one

or more of these visual cues exist, immediately request priority

handling from Air Traffic Control to facilitate a route or an altitude

change to exit the icing conditions.'' (This wording is slightly

different in the final rule for Aerospatiale airplanes because only one

visual cue is provided.) The FAA finds that this revision to the final

rules addresses the commenters' concerns with regard to the proposed

limitations.

One commenter poses various questions concerning the last sentence

of the first instruction listed in the procedures for exiting the

freezing rain/freezing drizzle environment in paragraph (a)(2) of the

proposals. (That sentence reads as follows: ``Asking for priority to

leave the area is fully justified under these conditions.'')

--What does the term ``priority'' provide a pilot when asking for

priority to leave icing conditions?

--What if there were three simultaneous requests for ``priority?''

--What Air Traffic Control procedures exist for treating an immediate

request for ``priority?''

--Where is the term ``priority'' defined?

The commenter states that confusion over terms that have not been

defined clearly by the FAA has partially resulted in accidents and

incidents. However, the commenter does not cite a specific case in

which this occurred.

The FAA has re-examined the last sentence of the first instruction

listed in the procedures for exiting the freezing rain/freezing drizzle

environment in paragraph (a)(2) of the proposals. The FAA has

reconsidered use of the term ``priority.'' The FAA finds that more

appropriate language that would be understood clearly by the flight

crew and Air Traffic Controllers should be used in that instruction.

Existing training for flight crews and Air Traffic Controllers

addresses priority handling of airplanes. However, the FAA will issue

additional information for Air Traffic Controllers to further clarify

priority handling of airplanes in severe icing conditions. The FAA

finds that the limitations specified in paragraph (a)(1) of the final

rules will result in the pilot taking appropriate steps to exit the

icing conditions. Therefore, the FAA finds that the sentence questioned

by the commenter may be removed from the final rules without affecting

safety. Accordingly, the FAA has removed that sentence from the final

rules.

Additionally, in order to use terminology in the procedures for

exiting the severe icing environment that is consistent with the

terminology used in the revised limitation and to simplify certain

language, the FAA has revised the first instruction of the procedures.

The revised instruction reads as follows: ``Immediately request

priority handling from Air Traffic Control to facilitate a route or an

altitude change to exit the icing conditions in order to avoid extended

exposure to flight conditions more severe than those for which the

airplane has been certificated.''

Comment 44. Request To Change the Note Concerning the Autopilot

One commenter, ATR, requests that the FAA revise the second note in

paragraph (a)(1) of the proposal for Aerospatiale airplanes. As

proposed, ATR believes the last sentence of the note is too

restrictive. ATR proposes the following: ``The autopilot may mask

tactile cues . . . characteristics. Therefore, when any ice is visible

on the airplane, the pilot should consider flying manually for short

periods in order to check the absence of any anomaly.''

Two commenters request that the FAA remove a similar note

concerning the autopilot from the proposals for airplanes other than

Aerospatiale

[[Page 20630]]

models. One of the commenters, JAL, states that the note contains

advisory information and should not appear in the Limitations Section

of an AFM.

The FAA concurs with ATR's comment that the last sentence of the

note is too restrictive; that sentence has been removed from the final

rules for all airplanes. However, the FAA does not agree with JAL's

contention that the explanation of the relationship between the

autopilot and the masking of tactile cues is inappropriate for

insertion in the Limitations Section of an AFM. On the contrary, the

FAA finds that inclusion of such information will increase the level of

understanding and, consequently, will increase the level of safety.

In light of this, the FAA finds that the note may be removed from

paragraph (a)(1) of the final rules for all airplanes; however, the

information contained in the first sentence of that note has been

combined with the autopilot limitation in paragraph (a)(1) of the final

rules. The final rules have been revised accordingly.

Comment 45. Requests To Remove Autopilot Limitation

Saab requests that the FAA revise the second limitation that

appears in paragraph (a)(1) of the proposal for Saab airplanes. As

proposed, this limitation indicates that use of the autopilot is

prohibited when any ice is observed forming aft of the protected

surfaces of the wing, or when unusual lateral trim requirements or

autopilot trim warnings are encountered. Saab asks that this autopilot

limitation be modified to take into consideration the autopilot system

design on these airplanes, which provides out-of-trim warnings;

therefore, the autopilot can be used up to the point where a warning is

triggered. Saab adds that the triggering point is early enough for the

warning to be taken, should the reason be ice build-up beyond the

protected surfaces. Additionally, there is no automatic disconnect if

the autopilot servo reaches its limit torque, which would prevent any

surprise to the pilot during an out-of-trim condition.

Another commenter, EMBRAER, requests that use of the autopilot not

be limited for EMBRAER Model EMB-120 series airplanes. The commenter

states that flight tests have demonstrated the safe ability of these

airplanes to depart a freezing rain/freezing drizzle condition with the

autopilot on.

Raytheon also objects to the autopilot limitation. Raytheon

suggests that a better approach is to inform the pilots of the nature

of ice accretion, and then let the pilots decide when to use the

autopilot. The commenter believes that prohibiting use of the autopilot

when any ice is observed aft of the protected surfaces of the wing is a

rigid requirement that takes away a valuable aid to the flight crew

when it may be needed most. Raytheon states that there is no evidence

that the autopilots on Beech aircraft would mask an icing related

control problem. The commenter points out that tests on those aircraft

disclosed no icing related control problem to mask. The commenter adds

that trying to anticipate every situation with an absolute prohibition

may lead to other unsafe conditions.

The FAA does not concur that the autopilot limitation should be

modified or removed from the AD's for any of the affected airplanes.

The limited amount of time the pilot is using manual controls instead

of the autopilot would not result in an unsafe condition. In normal

operational environments and conditions, the autopilot is a valuable

aid that reduces the workload of the flight crew. However, under

abnormal conditions (ice aft of the protected surfaces, unusual lateral

trim, or autopilot trim warnings), the autopilot will mask the build-up

of large or unusual control forces in one or more axes. Therefore, for

the short period of time necessary to exit severe icing conditions, the

safest course of action would be manual pilot control. Even if an

autopilot does not automatically disconnect, the pilot may choose to

disconnect the autopilot and could then be faced unexpectedly with

unusual control forces. These reasons also still hold true with

airplanes that have been flight tested with the ice shapes.

Since the issuance of the proposed rules, the FAA has re-examined

the autopilot limitation specified in paragraph (a)(1) of the

proposals. The FAA recognizes that clarification is necessary with

regard to its intent concerning that limitation. That limitation, as

specified in the proposals, states that use of the autopilot is

prohibited when any ice is observed forming aft of the protected

surfaces of the wing, or when unusual lateral trim requirements or

autopilot trim warnings are encountered. However, the FAA's intent

concerning that limitation is that the autopilot be disconnected when

the flight crew observes any of the visual cues identified in paragraph

(a)(1) of the AD's. The need to disconnect the autopilot arises when an

amount of ice accumulates that indicates the limits of the ice

protection equipment have been exceeded, regardless of the means by

which the flight crew becomes aware of the accumulation of ice.

Additionally, the FAA acknowledges that the autopilot limitation,

as proposed, could be misinterpreted to mean that the autopilot must be

disengaged when unusual lateral trim or autopilot trim warnings are

encountered, regardless of whether the airplane is in icing conditions.

However, the FAA only intended that the autopilot limitation apply

while the airplane is in icing conditions.

In light of this, the FAA has determined that the autopilot

limitation contained in paragraph (a)(1) of the final rules must be

revised. The FAA has changed that limitation to read as follows:

``Since the autopilot may mask tactile cues that indicate adverse

changes in handling characteristics, use of the autopilot is prohibited

when any of the visual cues specified above exist, or when unusual

lateral trim requirements or autopilot trim warnings are encountered

while the airplane is in icing conditions.'' (This wording is slightly

different in the final rule for Aerospatiale airplanes because only one

visual cue is provided.) This revision more accurately reflects the

FAA's intent and is, therefore, a logical outgrowth of the proposed

rules.

Comment 46. Request To Insert Procedures in Limitations or Abnormal

Procedures Section of AFM

One commenter suggests that operations in icing conditions that

exceed the capability of the airplane should be described in the

Limitations or Abnormal Procedures Section of the AFM, rather than in

the Normal Procedures Section, as specified in paragraph (a)(2) of the

proposals.

The FAA concurs partially. The FAA agrees that the Abnormal

Procedures Section may be an appropriate location for the procedures

for exiting severe icing conditions. However, the FAA does not agree

that such operational procedures should appear in the Limitations

Section of the AFM since such procedures are not limitations.

Additionally, upon further review, the FAA finds that AFM's may have

neither an Abnormal Procedures nor a Normal Procedures Section.

Consequently, to provide operators with flexibility as to where the

procedures specified in paragraph (a)(2) should be incorporated in the

AFM, that paragraph has been revised to require that the ``Procedures''

Section of the AFM be revised. This means that the procedures may be

inserted in the ``Normal Procedures,'' ``Abnormal Procedures,'' or

other ``Procedures'' Section of the AFM, as appropriate.

[[Page 20631]]

Comment 47. Request To Remove Duplicate Visual Cues

Two commenters indicate that certain visual cues specified in

paragraph (a)(2) of the proposals are duplicated in the ``Warning''

that is also contained in that paragraph. One commenter states that the

duplication of text reduces the impact of the message. Another

commenter questions whether the visual cues and procedures for exiting

the icing environment are intended to be part of the AFM material. The

FAA infers from these remarks that the commenters request that

duplicate text be removed.

Transport Canada Aviation requests that the ``Warning'' be removed

because indications of the possible hazard are progressive and may not

necessarily require immediate action from the pilot. The commenter

suggests that renaming this as a ``Caution'' may be more appropriate.

The FAA concurs partially. The FAA agrees that duplicate text

should be removed from the ``Warning'' section that appeared in the

proposals. The FAA finds that only one unique instruction appears in

the ``Warning'' in paragraph (a)(2) of the proposals: ``If the flaps

are extended, do not retract them until the airframe is clear of ice.''

Therefore, the FAA has added that instruction to the procedures for

exiting the severe icing environment in paragraph (a)(2) of the AD's.

The remainder of the ``Warning'' section that appeared in the proposals

has been removed from the final rules.

Comment 48. Request for Revision to Instruction for Flaps Extension

Saab requests that the FAA revise an instruction contained in the

procedures for exiting the freezing rain/freezing drizzle environment

in paragraph (a)(2) of the proposals. That instruction indicates to

``Avoid extending flaps during extended operation in icing conditions *

* *.'' Saab suggests the following: ``Do not extend flaps when holding

in conditions where ice is accreting on the airframe.'' Further, the

commenter asks that this instruction be inserted as a ``caution'' in

the Limitations Section of the AFM, rather than into the Normal

Procedures Section, as specified in the proposed rule. Saab believes

that it is imperative that the flaps not be extended in such cases.

Inserting the instruction into the Limitations Section, rather than the

Normal Procedures Section, would add strength to the requirement.

Another commenter states that this same instruction appears to be

in conflict with previously approved AFM revisions which state,

``Sustained flight in icing conditions is prohibited with flaps

extended.'' However, the commenter does not provide a suggestion for

rewording this instruction.

The FAA concurs that the procedures related to extension of the

flaps can be reworded somewhat. For clarification purposes, the FAA has

replaced the word ``avoid'' with ``do not'' in that procedure in

paragraph (a)(2) of the final rules. This revision eliminates the

conflict discussed by the second commenter. However, the FAA does not

agree that revising the remainder of the instruction, as suggested by

Saab, provides any additional clarification.

The FAA agrees that inserting the revised wording in the

Limitations Section of the AFM, rather than in the Normal Procedures

Section, would be acceptable; however, this would expand the scope of

the originally proposed rules and would necessitate reopening the

comment period to provide additional opportunity for public comment. In

light of the time required to complete the rulemaking process in

advance of the upcoming icing season and in consideration of the safety

issues addressed by these final rules, the FAA finds that the AD's

should be issued without additional delay. However, the FAA would

consider a request for approval of an alternative method of compliance,

in accordance with the provisions of this AD, to include this

information in the Limitations Section of an operator's AFM.

Transport Canada Aviation requests that this instruction be revised

to read as follows: ``Do not extend flaps during operation in icing

conditions, except for approach and landing. Operation with flaps

extended will result in a reduced wing angle-of-attack with the

possibility of ice forming on the upper surface further aft on the wing

than normal, possibly aft of the protected area.''

The FAA concurs partially. The FAA does not concur with the

commenter's suggested rewording to limit use of the flaps in all

operation in icing conditions except approach and landing. The wording

proposed in the AD's would affect use of the flaps only during extended

operation in icing conditions. The FAA finds that an amount of ice

sufficient to cause control problems is more likely to accumulate

during prolonged operations in icing conditions. Further, the FAA does

not concur that the words ``operation of the flaps can result in a

reduced angle-of-attack * * *'' should be changed to ``operation of the

flaps will result in a reduced angle-of-attack * * *'' in this

instruction. Operation with flaps extended does not always result in a

reduced angle-of-attack. For instance, during extension of the flaps

while the airplane is slowing, the angle-of-attack will increase.

The FAA concurs with the suggestion to include the words ``the

possibility of ice forming on the upper surface further aft * * *'' The

FAA acknowledges that under certain conditions the droplets will not

impinge further aft with a reduced angle-of-attack. The final rules

have been revised to add the words suggested by the commenter to the

sixth instruction specified in the procedures for exiting the severe

icing environment contained in paragraph (a)(2) of the AD's. That

revised instruction reads as follows: ``Do not extend flaps * * * with

the possibility of ice forming on the upper surface * * *''

Comment 49. Requests To Revise ``Caution'' Paragraph

One commenter asks that the heading, ``Caution,'' which appears in

paragraph (a)(2) of the proposals, be renamed ``Warning'' because this

section is intended to prevent loss of life or injury. Transport Canada

Aviation requests that the ``Caution'' section be changed to a note.

The commenter provides no justification.

The FAA concurs partially. The FAA does not concur that the

``Caution'' should be changed to a note because this section is

intended to prevent loss of life or injury. In light of this, the FAA

concurs with the commenter's request to rename the ``Caution'' section

``Warning.'' The FAA finds that ``Warning'' is a stronger term and

would be a more appropriate heading for the paragraph in question.

Additionally, the FAA finds that the ``Warning'' provides advisory

information that should precede the first limitation in paragraph

(a)(1) of the AD's. Accordingly, the FAA has revised the heading

``Caution'' to ``Warning'' in the final rules. In addition, the

``Warning'' has been placed at the beginning of paragraph (a)(1) of the

final rules. The FAA has determined that including this information in

the Limitations Section of the AFM will not impose an additional burden

on any operator, since it is informational only and does not

necessitate providing an additional opportunity for public comment.

Additionally, the commenter notes that an undefined term,

``extreme,'' is used in a sentence in the ``Caution'' paragraph of the

proposals, as follows: ``Flight in freezing rain, freezing drizzle, or

mixed icing conditions (supercooled liquid water and ice crystals) may

result in extreme ice build-up on protected surfaces * * *'' The FAA

infers from

[[Page 20632]]

this remark that the commenter asks that the word ``extreme'' be

removed from the ``Caution'' paragraph.

The FAA concurs. The FAA finds that removing the word ``extreme''

would not change the intent of the sentence and may eliminate

confusion. The word ``extreme'' has been removed from this section of

the final rule. In addition, for clarification purposes, the FAA has

revised the first sentence of the proposed ``Caution'' from ``Severe

icing comprises environmental conditions * * *'' to ``Severe icing may

result from environmental conditions * * *''

Comment 50. Request To Remove Visual Cues: Identification of Freezing

Rain/Freezing Drizzle

One commenter indicates that the cues provided in paragraph (a)(2)

of the proposals for identifying freezing rain/freezing drizzle

conditions are duplicated in material that appears in paragraph (a)(1)

of the proposals. The FAA infers from this remark that the commenter

requests that duplicative wording be removed from paragraph (a)(2) of

the proposed rules.

The FAA concurs. The FAA finds that the section entitled ``The

following shall be used to identify freezing rain/freezing drizzle

icing conditions'' is duplicated in material that appears in paragraph

(a)(1), and does not enhance the effectiveness of the AD's. Therefore,

that section has been removed from paragraph (a)(2) of the final rules

for all airplanes other than Aerospatiale Model ATR-42 and ATR-72

series airplanes.

Paragraph (a)(1) of the proposals for Aerospatiale airplanes

specified secondary indications for identifying possible freezing rain/

freezing drizzle conditions. The FAA recognizes that the flight crew

could have interpreted that paragraph to mean that if the secondary

indicators were observed, the airplane must be flown clear of the

severe icing conditions. However, the FAA's intent is that the flight

crew must immediately request priority handling to exit the icing

conditions only when the visual cue (ice on the side window) specified

in paragraph (a)(1) of the AD is observed.

Accordingly, the FAA has deleted the secondary indications of

possible severe icing conditions from paragraph (a)(1) of the final

rule for Aerospatiale airplanes. In addition, the FAA has removed the

visual cue (ice on the side window) from paragraph (a)(2) of the final

rule. The FAA has retitled the section containing the secondary

indications of possible severe icing as follows: ``The following may be

used as secondary indications of severe icing conditions.'' Further,

the last two secondary indicators contained in that section are

specified in the final rule in a section titled: ``The following

weather conditions may be conducive to severe in-flight icing.'' (This

change is explained further in Comment 51 below.)

Comment 51. Request To Remove Visual Cues: Identification of Possible

Freezing Rain/Freezing Drizzle

One commenter states that the word ``may'' in the following title,

which appears in paragraph (a)(2) of the proposals, is confusing: ``The

following may be used to identify possible freezing rain/freezing

drizzle conditions.'' The commenter indicates that AFM procedures

should provide a clear sequence of steps that must be followed and that

such procedures should be explicit; general advice, regardless of how

prudent, should be published elsewhere. The FAA infers from this remark

that the commenter asks that the cues that appear under this section be

deleted.

The FAA does not concur that this section should be removed. The

cues provided for identification of possible severe icing conditions

will alert the pilot to the possibility that unusual ice accretion may

develop. The FAA finds that the level of detail provided in the final

rules will increase the level of pilot awareness and, consequently,

will increase the level of safety over that which exists currently.

Therefore, the FAA has determined that it is appropriate to incorporate

this section in the AFM.

However, the FAA finds that clarification is necessary with regard

to the title of this section. The FAA finds that operators may

misinterpret that title, as proposed, to mean that this section

contains visual cues that should be used to identify possible severe

icing conditions prior to takeoff, dispatch, or release while the

airplane is on the ground. Additionally, the FAA finds that confusion

could result in differentiating between the weather conditions

specified in this section and the visual cues provided in paragraph

(a)(1) of the AD's. For clarification purposes, the FAA has revised the

title of this section to read as follows: ``The following weather

conditions may be conducive to severe in-flight icing.''

Comment 52. Request To Revise Air Temperature References

Transport Canada Aviation states that ambient temperature is

indicated as static air temperature (SAT), rather than outside air

temperature (OAT), for de Havilland Model DHC-8 series airplanes. The

FAA infers from this remark the commenter requests that the ambient

temperature that appears in the weather conditions specified in

paragraph (a)(2) of the proposals be expressed as SAT for those

airplanes.

The FAA does not concur. The FAA does not intend to specify which

specific indicator in the cockpit a pilot should use to determine the

ambient air temperature. The FAA intends that the pilot use whatever

means necessary to determine ambient air temperature.

However, since airplanes may have indicators other than OAT, the

FAA has replaced the words ``outside air temperature'' with ``ambient

air temperature'' in the weather conditions, and in the procedures for

exiting the severe icing environment, specified in paragraph (a)(2) of

these final rules to eliminate confusion concerning the need for a

specific type of indicator.

In addition, the FAA has re-examined the ambient temperature of +5

degrees Celsius that is specified in paragraph (a)(2) of the proposals.

The FAA has determined that this temperature is too high to be used as

a reliable indication of whether severe icing conditions may exist

during flight. The FAA finds that 0 degrees Celsius is a more

appropriate indication. The FAA has revised paragraph (a)(2) of the

final rules for all airplanes accordingly.

Comment 53. Request To Replace Reference to Droplets that Splash or

Splatter

JAL requests that the weather condition that pertains to ``droplets

that splash or splatter'' be removed from paragraph (a)(2) of the

proposals. JAL believes that this weather condition places too much

emphasis on subjective judgment. JAL states that normal rain conditions

will contain droplets that splash or splatter upon impact with the

windshield. JAL indicates that information included in its existing AFM

revisions, specified as follows, adequately addresses the issue:

``Prolonged operation in altitude bands where temperatures are near

freezing and heavy moisture is visible on the windscreen should be

avoided.''

The FAA does not concur that this weather condition should be

removed from the AD's. This weather condition must be used in

conjunction with the temperature specified as a means of identifying

severe in-flight icing conditions. The weather condition also will

alert the pilot to the possibility that unusual ice accretion may

develop. The FAA finds that the AFM information submitted by JAL does

not provide an equivalent alert to the pilot.

[[Page 20633]]

Comment 54. Request To Revise Procedures for Exiting Freezing Rain/

Freezing Drizzle

JAL requests that the procedures for exiting freezing rain/freezing

drizzle specified in paragraph (a)(2) of the proposals be restricted to

essential instructions that the flight crew must follow. JAL contends

that the procedures contained in the proposals are not written in the

appropriate format for AFM procedures, but are more representative of

advisory material. JAL also states that the current FAA- approved AFM

procedures for exiting freezing rain/freezing drizzle already provide

this essential information and conform to the existing style of the

AFM's. Transport Canada Aviation requests that the first instruction in

these procedures be revised to state only: ``Exit the freezing rain or

freezing drizzle conditions immediately.'' The commenter also requests

clarification of the terms ``extended exposure,'' as used in that

instruction.

The FAA concurs partially. The FAA has reviewed the procedures for

exiting the severe icing environment and finds that two of the

instructions contained in those procedures do not require the level of

detail provided in the proposed rules. The FAA finds that the

information concerning masking of control system forces is already

provided in the Limitations Section of the AFM. Therefore, the FAA has

revised the third instruction of those procedures to read as follows:

``Do not engage the autopilot.'' Additionally, the FAA has determined

that the flight crew need not be provided with instructions for

reducing the angle-of-attack because instructions such as this are

considered to be basic airmanship. Accordingly, the FAA has revised the

fifth instruction in the procedures for exiting the severe icing

environment to specify only information that is essential for the

flight crew. The revised instruction reads as follows: ``If an unusual

roll response . . . reduce the angle-of-attack.'' The FAA finds that,

for the remainder of the procedures for exiting, the additional level

of details provided in the final rules will increase the level of

understanding and, consequently, will increase the level of safety over

that which exists currently. The FAA finds that these procedures are

appropriate for insertion in the AFM's.

Regarding the terms ``extended exposure,'' the intent of that

instruction is to advise the flight crew that exiting the severe icing

conditions will minimize the exposure to flight conditions outside

those for which the airplane has been certificated. The FAA finds that

remaining in such conditions for a prolonged period may result in

accumulating an amount of ice sufficient to cause control problems. The

phrase ``to avoid extended exposure'' is only intended to explain to

the flight crew why severe icing conditions should be exited

immediately.

Raytheon questions the necessity to tell a commercial pilot not to

make any abrupt or excessive maneuvers if the aircraft is in the

position of having control difficulties. This instruction appears under

the heading ``Procedures for exiting the freezing rain/freezing drizzle

environment,'' which appears in paragraph (a)(2) of the proposals. The

commenter contends that this is a training issue and is not appropriate

for AFM procedures. The FAA infers from the commenter's remark that the

commenter requests that these instructions be eliminated from the

proposed rules.

The FAA does not concur. The FAA has determined that such

instructions provide beneficial guidance to the flight crew, which will

enhance the safety of the aircraft.

Saab requests that the FAA revise one of the instructions specified

in the procedures for exiting freezing rain/freezing drizzle specified

in the proposals. The instruction states that if an unusual roll

response or uncommanded control movement is observed, the angle-of-

attack should be reduced by increasing the airspeed or rolling the

wings level (if in a turn), and applying additional power, if needed.

Saab suggests that this instruction be revised to include the word

``aileron'' in the reference to uncommanded control movement. Saab

states further that in the case of wing ice beyond the protected

surfaces, the application of power may be appropriate to increase

airspeed/improve airflow. However, if ice has accrued on the wings

beyond the protected surfaces, there is a possibility that there also

is ice on the horizontal stabilizers. In this case, a sudden burst of

power may be detrimental. An uncommanded pitch control movement is

indicative of tail ice, which normally calls for a different action,

both concerning power as well as the handling of flaps, if extended.

Another commenter, Transport Canada Aviation, requests that the same

instruction be revised to include the word ``lateral'' in reference to

``uncommanded control movement,'' and to change the phrase ``or rolling

wings level'' to ``and rolling wings level.''

The FAA concurs partially. The FAA agrees that the correct

procedures for reducing the angle-of-attack is to increase the airspeed

and roll the wings level, if in a turn. However, as explained

previously, this portion of the procedure has been removed from the

final rules. The FAA does not agree that either ``lateral'' or

``aileron'' should be used to specify the type of uncommanded control

movement. The FAA finds that use of the term ``lateral'' may not be

understood by the flight crew. The FAA finds that including the word

``aileron'' may clarify which control surface is of concern; however,

the FAA has determined that use of a more general term, ``roll'' will

correctly specify the type of uncommanded control movement that is of

concern. The FAA has revised the fifth instruction in the procedures

for exiting the severe icing environment in paragraph (a)(2) of the

final rules accordingly. The revised instruction reads as follows: ``If

an unusual roll response or uncommanded roll control movement is

observed, reduce the angle-of-attack.''

In addition, the procedures for exiting the freezing rain/freezing

drizzle environment contained in the proposals did not specify to use

``a sudden burst of power'' when reducing the angle-of-attack. Rather,

the proposed procedure indicates to apply additional power, if needed,

to provide the desired flight path. However, as discussed previously,

the FAA has removed this reference from the final rules. In addition,

as explained previously, the FAA has revised the final rules to add the

word ``roll'' to describe the type of uncommanded control movement.

This revised wording addresses Saab's concern regarding increasing

power for a pitch anomaly.

Saab also notes that this instruction recommends a reduction in the

angle-of-attack and application of power, if needed. However, the next

instruction of the procedures indicates that reducing the angle-of-

attack may cause ice to build up beyond the protected areas of the

wing. Saab concludes that there is a conflict in that the proposed AD

would require that the angle-of- attack not be reduced or ice will

collect beyond the protected surfaces; however, the angle-of-attack

must be reduced if there is an unusual roll response or uncommanded

control movement.

The FAA does not concur with the commenter's contention that there

is a conflict in the AD's. Reducing the angle-of-attack by increasing

airspeed or rolling the wings level (if in a turn), and applying

additional power, if needed, is a procedure used to exit severe icing

conditions following an unusual roll response or uncommanded roll

control movement; whereas the instruction that involves not extending

the flaps during

[[Page 20634]]

extended operation in icing conditions is intended to prevent ice

build-up beyond the unprotected surfaces.

Raytheon asks for removal of the instruction to reduce the angle-

of-attack and apply additional power, if needed, in response to an

unusual roll response or uncommanded control movement. The commenter

states that these are normal instructions with respect to wing stall

and are inappropriate for inclusion in an AFM.

The FAA concurs partially. There may not be a stall warning

associated with uncommanded control movements in the case of encounters

with severe icing conditions. Since this is not a ``normal'' stall, the

flight crew may not recognize that normal stall recovery procedures

should be used. However, as stated previously, the instruction

referenced by the commenter has been deleted, in part, from the final

rules.

Raytheon also states that it is not appropriate to require contact

with Air Traffic Control as part of an AFM procedure since this is

already addressed in the Aeronautical Information Manual and in section

91.183 of the Federal Aviation Regulations (14 CFR 91.183). The FAA

infers from this statement that the commenter requests that the

instruction to contact Air Traffic Control should be removed from the

procedures for exiting severe icing conditions.

The FAA does not concur. The FAA is aware that this instruction is

contained in the references provided by the commenter. However, the FAA

finds that the importance of timely dissemination of this instruction

warrants its inclusion in the final rules. Inclusion of instructions of

this type is not without precedent; for example, similar information

also is specified in certain AFM's where the forward look windshear

system is addressed.

Comment 55. Request To Revise Procedures for Exiting the Severe Icing

Environment: Include Airplane- Specific Instructions

One commenter suggests that any action that might be necessary to

optimize aircraft performance and control in conditions of exceptional

icing, and exit from those conditions, should be determined separately

with each manufacturer; such procedures should be contained in the AFM

for each airplane model. The FAA infers from this remark that the

commenter requests that the FAA revise the procedures for exiting the

severe icing environment in each final rule to include airplane-

specific instructions.

The FAA agrees that procedures obtained from each individual

manufacturer should be considered and included in the final rules, if

appropriate. All manufacturers have been provided with an opportunity

to submit such procedures in response to the proposed rules. Some

manufacturers requested changes to the final rules. The FAA has revised

the final rules for those requests that were substantiated adequately.

Following issuance of the final rules, the FAA would consider a request

to include additional changes to the AFM revisions, in accordance with

the provisions of these AD's, provided that adequate justification is

presented to support such a request.

Comment 56. Revision of Procedures for Exiting the Severe Icing

Environment

The FAA has re-examined the section titled ``Procedures for exiting

the severe icing environment'' in paragraph (a)(2) of the proposals. As

proposed, that section states that if the visual cues used for

identifying ``possible'' freezing rain or freezing drizzle conditions

are observed, the flight crew should follow the procedures specified

for exiting those conditions. The FAA did not intend that the flight

crew use the procedures for exiting the severe icing environment when

the weather conditions specified in paragraph (a)(2) of these AD's are

observed. The FAA's intent is that the flight crew use those procedures

only when the visual cues identified in the Limitations Section of the

AFM are observed.

In order to eliminate any confusion, the FAA has revised the last

sentence of the first paragraph in the procedures for exiting the

severe icing environment. The FAA has removed the word ``possible''

from that sentence, and has added clarification that the visual cues

are specified in the Limitations Section of the AFM. The revised

sentence reads as follows: ``If the visual cues specified in the

Limitations Section of the AFM for identifying severe icing conditions

are observed, accomplish the following.'' (Operators should note that,

for Aerospatiale airplanes, the final rule specifies only one visual

cue, which involves ice on the side window.)

Comment 57. Request to Revise Cost Estimate

Transport Canada requests that the FAA provide an operational cost

estimate in the proposed AD's.

The FAA acknowledges the concern of the commenter. The FAA

recognizes that, in accomplishing the requirements of any AD, operators

may incur other costs in addition to the ``direct'' costs that are

reflected in the cost analysis presented in the AD preamble. However,

the cost analysis in AD rulemaking actions typically only includes such

direct costs. In the case of these AD's, for example, the requirements

are to revise the AFM to include certain information. How operators

actually ``implement'' that information thereafter (once it is placed

in the AFM) may vary greatly among them.

Further, because AD's require specific actions to address specific

unsafe conditions, they appear to impose costs that would not otherwise

be borne by operators. However, because of the general obligation of

operators to maintain and operate aircraft in an airworthy condition,

this appearance is deceptive. Attributing those costs solely to the

issuance of this AD is unrealistic because, in the interest of

maintaining and operating safe aircraft, prudent operators would

accomplish the required actions even if they were not required to do so

by the AD. In any case, the FAA has determined that direct and

incidental costs are still outweighed by the safety benefits of the AD.

The FAA points out that it is not required to do a full cost-

benefit analysis for each AD. AD's were explicitly exempted from the

Office of Management and Budget (OMB) coordination process described in

Section 6 of that Executive Order. As a matter of law, in order to be

airworthy, an aircraft must conform to its type design and be in a

condition for safe operation. The type design is approved only after

the FAA makes a determination that it complies with all applicable

airworthiness requirements. In adopting and maintaining those

requirements, the FAA has already made the determination that they

establish a level of safety that is cost-beneficial. When the FAA later

makes a finding of an unsafe condition in an aircraft and issues an AD,

it means that the original cost beneficial level of safety is no longer

being achieved and that the required actions are necessary to restore

that level of safety. Because this level of safety has already been

determined to be cost beneficial, and because the AD does not add an

additional regulatory requirement that increases the level of safety

beyond what has been established by the type design, a full cost-

benefit analysis for each AD would be redundant and unnecessary.

Comment 58. Requests to Delay Issuance of the Final Rules

Three commenters request that the FAA extend the comment period for

the proposed rules by 90 days. Each of the commenters request the

extension in order to complete a comprehensive

[[Page 20635]]

analysis of this issue. The commenters state their involvement in

focusing on ``. . . ther recent rulemaking activity, including the

Commuter Rule, flight crewmember training requirements, and proposed

rules covering flight crew flight, duty and test requirements . . .''

as a reason that did not allow complete analysis of the proposed AD's.

One commenter requests that implementation of the AD's be deferred

until further discussion with industry has been undertaken.

The FAA has reviewed these requests and, in consideration of the

importance and need for dissemination of this important information to

the aviation community, does not concur that the comment period should

be extended or issuance of the final rules be deferred until a later

date. Issuing the final rules will ensure that the information is

available, understood, and implemented by the aviation community before

the next icing season. For these reasons, the FAA has determined that

it is imperative that the information and actions contained in these

final rules be incorporated into the operators' AFM's immediately.

Conclusion

After careful review of the available data, including the comments

noted above, the FAA has determined that air safety and the public

interest require the adoption of the rule with the changes previously

described. The FAA has determined that these changes will neither

increase the economic burden on any operator nor increase the scope of

the AD.

Cost Impact

The FAA estimates that 169 airplanes in the U.S. registry will be

affected by this AD, that it will take approximately 1 workhour per

airplane to accomplish the required action, and that the average labor

rate is approximately $60 an hour. Since an owner/operator who holds at

least a private pilot's certificate as authorized by sections 43.7 and

43.11 of the Federal Aviation Regulations (14 CFR 43.7 and 43.11) can

accomplish the required action, the only cost impact upon the public is

the time it would take the affected airplane owner/operators to

incorporate the AFM revisions.

In addition, the FAA recognizes that this AD may impose operational

costs. However, those costs are incalculable because the frequency of

occurrence of the specified conditions and the associated additional

flight time cannot be determined. Nevertheless, because of the severity

of the unsafe condition addressed, the FAA has determined that

continued operational safety necessitates the imposition of these

costs.

Regulatory Impact

The regulations adopted herein will not have substantial direct

effects on the States, on the relationship between the national

government and the States, or on the distribution of power and

responsibilities among the various levels of government. Therefore, in

accordance with Executive Order 12612, it is determined that this final

rule does not have sufficient federalism implications to warrant the

preparation of a Federalism Assessment.

For the reasons discussed above, I certify that this action (1) is

not a ``significant regulatory action'' under Executive Order 12866;

(2) is not a ``significant rule'' under DOT Regulatory Policies and

Procedures (44 FR 11034, February 26, 1979); and (3) will not have a

significant economic impact, positive or negative, on a substantial

number of small entities under the criteria of the Regulatory

Flexibility Act. A copy of the final evaluation prepared for this

action is contained in the Rules Docket. A copy of it may be obtained

by contacting the Rules Docket at the location provided under the

caption ADDRESSES.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Incorporation by

reference, Safety.

Adoption of the Amendment

Accordingly, pursuant to the authority delegated to me by the

Administrator, the Federal Aviation Administration amends part 39 of

the Federal Aviation Regulations (14 CFR part 39) as follows:

PART 39--AIRWORTHINESS DIRECTIVES

1. The authority citation for part 39 continues to read as follows:

Authority: 49 USC 106(g), 40113, 44701.

Sec. 39.13 [Amended]

2. Section 39.13 is amended by adding a new airworthiness directive

(AD) to read as follows:

96-09-11 De Havilland: Amendment 39-9587; Docket No. 96-CE-01-AD.

Applicability: Models DHC-6-1, DHC-6-100, DHC-6-200, and DHC-6-

300 airplanes (all serial numbers), certificated in any category.

Note 1: This AD applies to each airplane identified in the

preceding applicability provision, regardless of whether it has been

modified, altered, or repaired in the area subject to the

requirements of this AD. For airplanes that have been modified,

altered, or repaired so that the performance of the requirements of

this AD is affected, the owner/operator must request approval for an

alternative method of compliance in accordance with paragraph (d) of

this AD. The request should include an assessment of the effect of

the modification, alteration, or repair on the unsafe condition

addressed by this AD; and, if the unsafe condition has not been

eliminated, the request should include specific proposed actions to

address it.

Compliance: Required as indicated, unless accomplished

previously.

To minimize the potential hazards associated with operating the

airplane in severe icing conditions by providing more clearly

defined procedures and limitations associated with such conditions,

accomplish the following:

(a) Within 30 days after the effective date of this AD,

accomplish the requirements of paragraphs (a)(1) and (a)(2) of this

AD.

Note 2: Operators must initiate action to notify and ensure that

flight crewmembers are apprised of this change.

(1) Revise the FAA-approved Airplane Flight Manual (AFM) by

incorporating the following into the Limitations Section of the AFM.

This may be accomplished by inserting a copy of this AD in the AFM.

``WARNING

Severe icing may result from environmental conditions outside of

those for which the airplane is certificated. Flight in freezing

rain, freezing drizzle, or mixed icing conditions (supercooled

liquid water and ice crystals) may result in ice build-up on

protected surfaces exceeding the capability of the ice protection

system, or may result in ice forming aft of the protected surfaces.

This ice may not be shed using the ice protection systems, and may

seriously degrade the performance and controllability of the

airplane.

During flight, severe icing conditions that exceed

those for which the airplane is certificated shall be determined by

the following visual cues. If one or more of these visual cues

exists, immediately request priority handling from Air Traffic

Control to facilitate a route or an altitude change to exit the

icing conditions.

--Unusually extensive ice accreted on the airframe in areas not

normally observed to collect ice.

--Accumulation of ice on the upper surface of the wing aft of the

protected area.

--Accumulation of ice on the propeller spinner farther aft than

normally observed.

Since the autopilot may mask tactile cues that indicate

adverse changes in handling characteristics, use of the autopilot is

prohibited when any of the visual cues specified above exist, or

when unusual lateral trim requirements or autopilot trim warnings

are encountered while the airplane is in icing conditions.

All icing detection lights must be operative prior to

flight into icing conditions at night. [NOTE: This supersedes any

relief provided by the Master Minimum Equipment List (MMEL).]''

(2) Revise the FAA-approved AFM by incorporating the following

into the

[[Page 20636]]

Procedures Section of the AFM. This may be accomplished by inserting

a copy of this AD in the AFM.

``THE FOLLOWING WEATHER CONDITIONS MAY BE CONDUCIVE TO SEVERE IN-FLIGHT

ICING:

Visible rain at temperatures below 0 degrees Celsius

ambient air temperature.

Droplets that splash or splatter on impact at

temperatures below 0 degrees Celsius ambient air temperature.

PROCEDURES FOR EXITING THE SEVERE ICING ENVIRONMENT:

These procedures are applicable to all flight phases from

takeoff to landing. Monitor the ambient air temperature. While

severe icing may form at temperatures as cold as -18 degrees

Celsius, increased vigilance is warranted at temperatures around

freezing with visible moisture present. If the visual cues specified

in the Limitations Section of the AFM for identifying severe icing

conditions are observed, accomplish the following:

Immediately request priority handling from Air Traffic

Control to facilitate a route or an altitude change to exit the

severe icing conditions in order to avoid extended exposure to

flight conditions more severe than those for which the airplane has

been certificated.

Avoid abrupt and excessive maneuvering that may

exacerbate control difficulties.

Do not engage the autopilot.

If the autopilot is engaged, hold the control wheel

firmly and disengage the autopilot.

If an unusual roll response or uncommanded roll control

movement is observed, reduce the angle-of-attack.

Do not extend flaps during extended operation in icing

conditions. Operation with flaps extended can result in a reduced

wing angle-of-attack, with the possibility of ice forming on the

upper surface further aft on the wing than normal, possibly aft of

the protected area.

If the flaps are extended, do not retract them until

the airframe is clear of ice.

Report these weather conditions to Air Traffic

Control.''

(b) Incorporating the AFM revisions, as required by this AD, may

be performed by the owner/operator holding at least a private pilot

certificate as authorized by section 43.7 of the Federal Aviation

Regulations (14 CFR 43.7), and must be entered into the aircraft

records showing compliance with this AD in accordance with section

43.11 of the Federal Aviation Regulations (14 CFR 43.11).

(c) Special flight permits may be issued in accordance with

sections 21.197 and 21.199 of the Federal Aviation Regulations (14

CFR 21.197 and 21.199) to operate the airplane to a location where

the requirements of this AD can be accomplished.

(d) An alternative method of compliance or adjustment of the

compliance time that provides an acceptable level of safety may be

used if approved by the Manager, Small Airplane Directorate, FAA,

1201 Walnut, suite 900, Kansas City, Missouri 64106. The request

shall be forwarded through an appropriate FAA Maintenance Inspector,

who may add comments and then send it to the Manager, Small Airplane

Directorate.

Note 3: Information concerning the existence of approved

alternative methods of compliance with this AD, if any, may be

obtained from the Small Airplane Directorate.

(e) All persons affected by this directive may examine

information related to this AD at the FAA, Central Region, Office of

the Assistant Chief Counsel, Room 1558, 601 E. 12th Street, Kansas

City, Missouri 64106.

(f) This amendment (39-9587) becomes effective on June 11, 1996.

Issued in Kansas City, Missouri, on April 24, 1996.

Henry A. Armstrong,

Acting Manager, Small Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 96-10728 Filed 5-1-96; 3:23 pm]

BILLING CODE 4910-13-P