Airworthiness Directives; Fairchild Model F-27 and FH-227 Series Airplanes

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-143-AD; Amendment 39-11298; AD 99-19-09]

RIN 2120-AA64

Airworthiness Directives; Fairchild Model F-27 and FH-227 Series

Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

-----------------------------------------------------------------------

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

applicable to certain Fairchild Model F-27 and FH-227 series airplanes,

that requires revising the Airplane Flight Manual (AFM) to include

requirements for activation of the airframe pneumatic deicing boots.

This amendment is prompted by reports of inflight incidents and an

accident that occurred

[[Page 63592]]

in icing conditions where the airframe pneumatic deicing boots were not

activated. The actions specified by this AD are intended to ensure that

flightcrews activate the pneumatic wing and tail deicing boots at the

first signs of ice accumulation. This action will prevent reduced

controllability of the aircraft due to adverse aerodynamic effects of

ice adhering to the airplane prior to the first deicing cycle.

EFFECTIVE DATE: December 27, 1999.

ADDRESSES: Information pertaining to this rulemaking action may be

examined at the Federal Aviation Administration (FAA), Transport

Airplane Directorate, Rules Docket, 1601 Lind Avenue, SW., Renton,

Washington; or at the FAA, Engine and Propeller Directorate, New York

Aircraft Certification Office, 10 Fifth Street, Third Floor, Valley

Stream, New York.

FOR FURTHER INFORMATION CONTACT: Ezra Sasson, Aerospace Engineer,

Systems and Flight Test Branch, ANE-172, FAA, Engine and Propeller

Directorate, New York Aircraft Certification Office, 10 Fifth Street,

Third Floor, Valley Stream, New York 11581; telephone (516) 256-7520;

fax (516) 256-2716.

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

Aviation Regulations (14 CFR part 39) to include an airworthiness

directive (AD) that is applicable to certain Fairchild Model F-27 and

FH-227 series airplanes was published in the Federal Register on July

16, 1999 (64 FR 38322). That action proposed to require revising the

Airplane Flight Manual (AFM) to include requirements for activation of

the airframe pneumatic deicing boots.

Related Proposals

In addition to the proposed rule described previously, in June

1999, the FAA issued 18 other similar proposals that address the

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

listing of all 19 proposed rules). Those 18 proposals also were

published in the Federal Register on July 16, 1999. (Docket 99-NM-153-

AD, for Fokker Model F-27 Mark 100, 200, 300, 400, 500, 600, and 700

series airplanes, was also issued as a supplemental notice of proposed

rulemaking, and published in the Federal Register on August 6, 1999.)

This final rule contains the FAA's responses to all relevant public

comments received for each of these proposed rules.

------------------------------------------------------------------------

Federal register

Manufacturer airplane model Number citation

------------------------------------------------------------------------

Cessna Aircraft Company Models 99-NM-136-AD 64 FR 38374

500, 550, and 560 Series

Airplanes.

Sabreliner Corporation Models 99-NM-137-AD 64 FR 38358

40, 60, 70, and 80 Series

Airplanes.

Gulfstream Aerospace Model G- 99-NM-138-AD 64 FR 38341

159 Series Airplanes.

McDonnell Douglas Models DC-3 99-NM-139-AD 64 FR 38325

and DC-4.

Mitsubishi Heavy Industries 99-NM-140-AD 64 FR 38371

Model YS-11 and YS-11A Series

Airplanes.

Gulfstream American (Frakes 99-NM-141-AD 64 FR 38355

Aviation) Model G-73 (Mallard)

and G-73T Series Airplanes.

Lockheed, Models L-14 and L-18 99-NM-142-AD 64 FR 38338

Series Airplanes.

Fairchild Models F-27 and FH- 99-NM-143-AD 64 FR 38322

227 Series Airplanes.

Aerospatiale Models ATR-42/ATR- 99-NM-144-AD 64 FR 38368

72 Series.

Jetstream Model BAe ATP 99-NM-145-AD 64 FR 38351

Airplanes.

Jetstream Model 4101 Airplanes. 99-NM-146-AD 64 FR 38335

British Aerospace Model HS 748 99-NM-147-AD 64 FR 38319

Series Airplanes.

Saab Model SF340A/SAAB 340B/ 99-NM-148-AD 64 FR 38365

SAAB 2000 Series Airplanes.

CASA Model C-212/CN-235........ 99-NM-149-AD 64 FR 38348

Dornier Model 328-100 Series 99-NM-150-AD 64 FR 38332

Airplanes.

Lockheed Model 1329-23 and 1329- 99-NM-151-AD 64 FR 38316

25 (Lockheed Jetstar) Series

Airplanes.

de Havilland Model DHC-7/DHC-8 99-NM-152-AD 64 FR 38362

Series Airplanes.

Fokker Model F-27 Mark 100/200/ 99-NM-153-AD 64 FR 42870

300/400/500/600/700/050 Series

Airplanes.

Short Brothers Model SD3-30/SD3- 99-NM-154-AD 64 FR 38329

60/SD3-SHERPA Airplanes.

------------------------------------------------------------------------

Comments

Interested persons have been afforded an opportunity to participate

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

the following comments received.

1. Support for the Rule

One commenter supports the proposed rule.

2. Request To Withdraw the Proposal: No Unsafe Condition

Several commenters request that the proposal be withdrawn because

no unsafe condition exists on certain

[[Page 63593]]

airplanes. One of these commenters states that the FAA is merely

speculating that the proposed Airplane Flight Manual (AFM) revision

will improve safety. Further, the commenter contends that the FAA

cannot substantiate that the proposed AFM revision will prevent ice

bridging. This same commenter also asks if the FAA met its own

standards by testing the proposed procedure on each of the affected

airplanes.

The FAA does not concur that no unsafe condition exists. As

discussed in the preamble of the proposed rule, the FAA has reviewed

the icing-related incident history of certain airplanes, and has

determined that icing incidents may have occurred because pneumatic

deicing boots were not activated at the first evidence of ice

accretion. As a result, the handling qualities or the controllability

of the airplane may have been reduced due to the accumulated ice. The

FAA also discussed an accident that occurred as a result of the failure

of the flightcrew to activate the wing and tail pneumatic deicing

boots.

Although there may have been no reported cases of incidents or

accidents on a specific airplane model, the potential still exists for

reduced controllability of all airplanes equipped with pneumatic

deicing boots due to adverse aerodynamic effects of ice adhering to the

airplane. This AD addresses this unsafe condition.

Further, ice bridging of deicing boots was considered during

development of the proposed rule. A broad representation of the

aviation community was consulted, including airframe manufacturers, air

carriers, airline pilot associations, airplane owner associations,

deicing boot manufacturers, and National Aeronautics and Space

Administration (NASA). Also, articles readily accessible by the general

piloting community solicited operational information concerning ice

bridging of deicing boots. The FAA considers that the general consensus

of the aviation community is that little or no evidence exists of ice

bridging of deicing boots with current deicing boot designs, and ice

that is not shed after the initial boot cycle continues to increase in

thickness and sheds during subsequent cycles.

In addition, many airplanes equipped with pneumatic deicing boots

to protect the engine are operated when icing conditions are present,

i.e., visible moisture and a specific temperature are observed. As

discussed in Comment #3 (following this response), at least two

airplane manufacturers have issued AFM's that contain procedures to

activate the deicing boots at the first sign of ice accumulation. The

FAA is unaware of any ice bridging problems associated with early

operations of either the airfoil or engine pneumatic deicing boots.

In response to the commenter's question regarding the FAA meeting

its own standards, the FAA infers that the commenter is requesting the

basis for the FAA's determination that the proposed procedures are

safe. Most aircraft certification programs have not considered the

reduced controllability of the aircraft due to adverse aerodynamic

effects of ice adhering to the pneumatic boots. The requirements of

this AD (activation of the deicing boot system at the first sign of ice

formation anywhere on the aircraft, or upon annunciation from an ice

detector system, whichever occurs first, along with the periodic

cycling of the boots) will minimize the ice accretions and thereby

reduce the adverse aerodynamic effects.

3. Request To Withdraw the Proposal: Possible Adverse Effects of

Residual Ice

Several commenters state that deicing boots do the best job of

shedding ice on a single cycle, if ice is permitted to accrete to \1/2\

or \1/4\ inch before activation of the boots. One of these commenters

further contends that the effect of continuous cycling in auto mode may

not produce a clean shed of ice on each activation, and that residual

ice must be taken into consideration before any revision to the AFM is

required. Another commenter states that, although operation in the

continuous mode upon first indication of ice accretion would eliminate

the problem of identification of accretion, the commenter is concerned

that there would then be a potential for degraded performance due to

residual ice.

The FAA does not concur that the proposal should be withdrawn

because of concerns over residual ice. Operation of pneumatic deicing

boots typically results in persistent ice accretions on the boot

surfaces, even when \1/2\ to \1/4\ inch of ice is allowed to accrete

prior to activation of the boots. The persistent residual and inter-

cycle ice accretions typically result in adverse aerodynamic effects

and degraded airplane flying qualities. Activation of the wing and tail

pneumatic deicing boots at the first sign of ice accretion, or at the

annunciation of an ice detector system and periodic operation of the

deicing boots will also result in persistent ice accretions. However,

the proposed procedure will minimize the residual and intercycle ice

accretions because the ice will be shed when the minimum thickness or

mass required for shedding is reached. The residual and intercycle ice

accretion thickness resulting from this procedure is less than the ice

accretion thickness typically recommended prior to operation of the

pneumatic deicing boot. Adverse airplane flying qualities resulting

from ice accretions typically are affected by the thickness, shape,

texture, and location of the ice accretion.

At least two airplane manufacturers have issued AFM's that contain

procedures to activate the deicing boots at the first sign of ice

accumulation. Those two airplane models have different wing and

stabilizer design characteristics and different deicing boot

configurations. Further, those two airplane models represent a large

proportion of the airplane fleet equipped with pneumatic deicing boots.

The FAA has received no reports indicating any adverse effects of

residual ice resulting from early activation of the deicing boots for

these airplane designs.

In addition, a number of airplane models are equipped with deicing

boot systems that include automatic operating modes, wherein the boots

automatically cycle at specific time intervals after being activated.

This automatic cycling has surely resulted in operation of the boots

with less than the recommended thickness of ice accreted. The FAA has

received no reports indicating any adverse effects resulting from the

use of the automatic mode.

4. Request To Withdraw or Delay: Develop More Data

Several commenters request that the FAA delay issuance of the rule

until more data are developed and reviewed. Certain of these commenters

also state that at the public meeting on icing (February 2-4, 1999),

the consensus was that a uniform procedure cannot be adopted for all

airplanes. That is, a ``blanket'' proposal for numerous airplanes

(regardless of design) is inappropriate without specific consideration

for the individual designs. Another one of these commenters points out

that each airplane model is unique and that the operating instructions

for the ice protection system for one airplane model may not be

appropriate for another airplane model. That commenter further adds

that the airframe manufacturer is in the best position to determine

appropriate limitations.

Another one of the commenters requests that, if the proposal is not

withdrawn, the issuance of any rulemaking be delayed since certain

language of the requirements of the AD is confusing.

[[Page 63594]]

The FAA does not concur that a delay in issuing this action is

appropriate. The FAA concurs that the airframe manufacturers present at

the February public meeting did not support a common procedure for the

operation of deicing boots. However, as mentioned previously, there

have been no adverse reports on the airplane fleet equipped with

pneumatic deicing boots that operate the boots at the first sign of ice

accretion. With the exception of ``older'' pneumatic boots (reference

comment #7, below), the FAA finds that a common procedure for boot

operation is appropriate. The FAA has determined that the common

procedures for operation of deicing boots as required by this AD

(activation of the deicing boot system at the first sign of ice

formation anywhere on the aircraft, or upon annunciation of an ice

detector system, whichever occurs first, and periodic cycling of the

boots) will minimize the ice accretions and thereby reduce the adverse

aerodynamic effects.

To withdraw or delay this AD would be inappropriate since the FAA

has determined that an unsafe condition exists, and that the required

AFM revision must be accomplished to ensure continued safety of the

fleet. The fact that other data may be developed at a later time does

not negate the FAA's responsibility to address the existing identified

unsafe condition in a timely manner. No change is necessary to the

final rule in this regard.

The FAA is unable to respond to one commenter's statement that

certain language of the proposal was confusing since no example was

specified.

5. Request To Withdraw Proposals for Certain Airplanes

Three commenters, all airframe manufacturers, request that the

proposal be withdrawn for several airplane models [British Aerospace

Model ATP airplanes, British Aerospace Model HS 748 airplanes, Dornier

Model 328-100 series airplanes, and deHavilland Model DHC-7/DHC-8

series airplanes] since they have been certified to be in compliance

with part 25 of the Federal Aviation Regulations (14 CFR 25.1419).

Additionally, the commenters point out that those airplanes have been

certificated in accordance with the appropriate foreign civil

airworthiness authorities. The commenters further explain that service

experience of those airplanes does not indicate any deficiencies with

regard to handling and performance due to airframe accreted ice. In

conclusion, the commenters state that, in the absence of any evidence

to suggest deficiencies regarding this subject, they cannot support the

intent of the rule.

The FAA acknowledges that an airplane model may have design

characteristics that mitigate the adverse airplane flying qualities

resulting from ice accretion on deicing boot surfaces. As discussed in

the proposal for this AD, the FAA has previously requested that

interested persons provide information on icing system design and

operations procedures concerning flight during icing conditions. The

request also asked manufacturers, who are in the best position to

determine those operating procedures, to provide data showing that

their aircraft have safe operating characteristics with ice accreted on

the protected surfaces (boots). That information was requested

specifically by letter on October 1, 1998, to certain manufacturers of

airplanes certified in accordance with part 25 of the Federal Aviation

Regulations (14 CFR part 25). Except as discussed in Item 6 of the

comment section of this final rule, no other information received

caused the FAA to reconsider that an unsafe condition may exist, or

that a revision of the AFM, such as required by this AD, was unsafe for

those airplanes.

Additionally, similar information was specifically requested in the

discussion section of the proposed rule. Of the comments to the

proposal that were received by the FAA, no additional data was included

for Dornier Model 328-100 series airplanes, or de Havilland Model DHC-

7/DHC-8 series airplanes that caused the FAA to reconsider the previous

conclusion that an unsafe condition exists. Further, no data was

provided to indicate that the proposal to require activation of wing

and tail pneumatic deicing boots at the first sign of ice accretion or

annunciation of an ice detector system was unsafe for any particular

airplane model.

United Kingdom Accident Investigation Board Preliminary Report EWC

91/18 indicated that, while on climb to 16,000 feet in the vicinity of

Oxford, England, on August 11, 1991, a British Aerospace Model ATP

airplane suffered a significant degradation of flying qualities and

propeller icing. According to that report, the deicing boots of the

airplane were not activated, and the airplane stalled, experienced

severe uncontrolled roll oscillations, severe vibration that rendered

the electronic flight instruments partially unreadable, and developed a

high rate of descent. The deicing boots were finally activated and

control of the airplane was regained after a loss of 3,500 feet in

altitude. The report identified causal factors of the incident which

included rapid accumulation of glaze ice that was not evident to the

flightcrew, difficulty of the flightcrew to visually gauge the ice

accretion thickness on the wing's leading edge, and propeller

vibrations that disguised the onset of wing stall. Even though this

incident occurred outside of the United States, and although this

airplane model demonstrated acceptable in-flight icing airworthiness

relative to FAA and Joint Airworthiness Authorities (JAA) requirements,

the incident illustrates the vulnerability of this airplane model to

the safety condition addressed by this AD.

One commenter, British Aerospace, has requested until October 20,

1999, to provide additional data to substantiate that the Model ATP

airplanes and Model HS 748 airplanes can safely operate with ice

accumulations on the protected surfaces. As discussed previously and in

the NPRM, the FAA considers that this same vulnerability exists on all

airplanes equipped with pneumatic deicing boots.

In the interest of safety, the FAA finds that it is not prudent to

delay issuance of the final rules on those airplane models. However,

British Aerospace and any other manufacturer is encouraged to request

approval of an alternative method of compliance with the airworthiness

directive based on substantiating data indicating that a particular

aircraft can safely be operated with the ice that would accumulate on

the protected surfaces prior to activation of the ice protection

system.

6. Request To Withdraw the Proposal for Certain Other Airplanes

Two manufacturers request that the proposals regarding Cessna Model

500, 501, 550, 551, and 560 series airplanes, and British Aerospace

(Jetstream) Model 4101 airplanes be withdrawn. The manufacturers advise

that the testing summarized in their comments provides evidence that

the current procedures provide a safe method to operate those airplane

models. The manufacturers conclude that, based on the service history

and data provided to the FAA, the proposed AFM revision for those

models is unnecessary.

The FAA concurs that the notice of proposed rulemaking for Cessna

Model 500, 501, 550, 551, and 560 series airplanes should be withdrawn

based on the following information. The manufacturer performed a

complete evaluation of the stall and handling characteristics with

simulated ice shapes on the Model 550 (Bravo) series airplanes. Stall

speeds and warning margins were evaluated with a \1/2\-inch glaze ice

shape and with an ice shape

[[Page 63595]]

associated with the system failure. This \1/2\-inch ice shape simulated

the ice shape prior to deicing boot activation. Maneuver margin testing

consisted of left and right 40-degree bank turns. Stall characteristics

were evaluated with a \1/2\-inch rime ice shape configuration. Stall

characteristic testing consisted of wings level and 30-degree bank

turns. At the conclusion of the testing it was determined that the

airplane had an acceptable stall warning margin with ice shapes

present. The manufacturer maintains that Model 500/501, Model 550/551,

and Model 550 (Bravo) series airplanes all use a common wing airfoil

with some minor differences in span and wing loading. These aircraft

also use a common tail configuration (airfoil, span, and leading edge

sweep).

Additionally, the FAA reviewed the Type Inspection Report (TIR) for

Model 550 (Bravo) series airplane testing and found that ice shapes

were placed on both the protected and unprotected surfaces.

The Model 560 (Ultra) series airplanes underwent an extensive ice

shape stall investigation. This investigation consisted of stall

testing of the baseline airplane and the airplane with the most adverse

simulated intercycle ice shapes. The ice shapes consisted of \1/2\-inch

shapes on the surfaces protected by boots and 3-inch shapes on

unprotected flight surfaces. The stall speeds determined by this

testing were incorporated into the Safeflight Angle of Attack computer

to increase the stall warning margin during flight in icing conditions.

The Model 560 series airplanes angle of attack computer was also

updated to incorporate a normal mode and an ice mode stall warning

system. The changes to the angle of attack computer on Model 560 and

560 (Ultra) series airplanes were proposed by Rules Docket No. 98-NM-

312-AD.

The FAA notes that extensive testing of Model 550 and 560 series

airplanes (in which acceptable stall protection and maneuver margins at

operational speeds were demonstrated with expected ice accretion on the

deicing boot surfaces) indicates that these airplanes can safely

operate with ice accretions associated with the AFM normal operations

procedures of the deicing boots. These attributes demonstrate that

Model 550 and 560 series airplanes satisfactorily address the unsafe

condition addressed by this AD. Since Model 500 series airplanes are

similar to Model 550 series airplanes, the Model 500 series airplanes

also satisfactorily address the unsafe condition addressed by this AD.

The FAA also notes that testing of Model 560 series airplanes revealed

problems in the stall warning margin for flight in icing conditions

that were addressed by previously issued airworthiness directives.

The FAA also concurs that the notice of proposed rulemaking for

British Aerospace Jetstream Model 4101 airplanes should be withdrawn

based on the following information. In response to the FAA's October 1,

1998, letter (discussed previously), British Aerospace submitted a

summary of the handling and performance flight test results that were

produced during the original flight in icing certification. This

summary was referenced in their response to the proposed rulemaking.

The commenter volunteered to provide any reports referenced in the

summary. The FAA requested and subsequently received copies of the full

handling and performance flight test results for certification in the

icing conditions specified in Appendix C of part 25 of the Federal

Aviation Regulations (14 CFR part 25), and the JAA draft issue of

AMJ25.1419, which was used as guidance for compliance with JAR/FAR

25.1419. The FAA reviewed these reports and guidance material and finds

that the Jetstream 4101 airplane was adequately tested with a variety

of natural ice accretions on both the protected and unprotected

surfaces. Handling and performance flight test was accomplished for the

following: Normal Operation of the Deicing Boots, \1/2\- to \3/4\-inch

of ice on the protected wing leading edges and up to 3 inches of ice on

unprotected leading edges; Simulated Failure of the Deicing Boots,

approximately 1 to 1\1/2\ inches of ice on all leading edges; Ice

Accreted During the Take-off Phase, a thin rough layer of ice accreted

during the initial take-off phase to 400 feet, prior to operation of

deicing boots.

These ice accretion depths were established to address the

following: Ice accreted during the rest-time of a deicing cycle,

delayed operation or failure of the system, and residual ice

accumulations. The flight testing examined stall speeds, stall warning

margins, stall characteristics, maneuver margins, longitudinal

controllability, flap configuration changes, ability to trim,

susceptibility to tailplane stall, and longitudinal, lateral, and

directional stability. The angles of attack for activation of the stall

warning system and stall identification system (i.e., stick shaker or

stick pusher) are reset to lower values (i.e., higher speeds) for

flight in icing and safe flight speeds (minimum operating speeds)

established accordingly. Affected AFM performance information was

derived for icing conditions based on the higher operating speeds, in

accordance with JAA draft AMJ25.1419.

The Cessna and British Aerospace aircraft models discussed in this

comment have been tested and, where appropriate, changes have been made

to ensure the airplanes are safe for operations with ice accretions on

the protected surfaces. Without this type of testing and

substantiation, the FAA must conclude the aircraft affected by this

final rule may be subject to adverse aerodynamic effects due to ice

accretions on the protected surfaces prior to deicing boot operation.

Other manufacturers may also develop the necessary data to substantiate

that their airplanes are safe with these accretions and request

approval of an alternative method of compliance.

7. Request To Differentiate Between ``Modern'' Boot Systems and

``Older'' Boot Systems

Several commenters request that the difference between the

``older'' boot systems and the ``modern'' boot systems be explained.

These commenters express concern that although both systems are

addressed in the proposal, there may not be a sound technical reason to

apply the requirements of the proposal to both types of boot systems.

The FAA acknowledges that definitions of ``older'' and ``modern''

pneumatic boot systems should be provided. Therefore, for the purposes

of this AD, ``modern'' pneumatic boot systems may be characterized by

short segmented, small diameter tubes, which are operated at relatively

high pressures [18-23 pounds per square inch (psi)] by excess bleed air

that is provided by turbine engines. ``Older'' pneumatic boot systems

may be characterized by long, uninterrupted, large diameter tubes,

which were operated at low pressures by engine driven pneumatic pumps

whose pressure varied with engine revolutions per minute (rpm). This

low pressure coupled with long and large diameter tubes caused early

de-ice systems to have very lengthy inflation and deflation cycles and

dwell times. (Dwell time is the period of time that the boot remains

fully expanded following the completion of the inflation cycle until

the beginning of the deflation cycle.)

8. Request To Withdraw the Proposal for Airplanes With ``Older'' Boots

Two commenters request that the proposed rules applying to

Gulfstream Model G-159 series airplanes and McDonnell Douglas Model DC-

3 and DC-4 series airplanes be withdrawn. Both commenters state that

those airplane models do not meet the

[[Page 63596]]

common definition of the word ``modern.'' (See Comment #7 of this final

rule for a definition of ``modern'' as used in this AD.) One commenter

states that the current AFM specifically directs the flightcrew to wait

for \1/4\-inch of ice before activating the boots. Further, the

commenter asserts that the current procedure was developed during

certification and is the basis for the airplane's approval for flight

into known icing. Additionally, the commenters assert that the in-

service safety records for more than 40 years indicates that the

existing procedures are appropriate for these airplanes. The commenter

concludes that the proposed AFM revision is in direct opposition to the

certification findings.

The FAA acknowledges that early activation of the ``older''

pneumatic deicing boots may create the hazard of ice bridging on the

``older'' systems. As discussed in Comment #2 previously, ``older''

boots may be susceptible to ice bridging, and the FAA concurs that

requiring the activation of the boots at the first sign of icing may

actually introduce an unsafe condition on those airplanes. In order to

address this issue, the FAA is taking the following steps. First, to

accommodate certain airplane models of the fleet (i.e., Gulfstream

Model G-159 series airplanes and McDonnell Douglas Model DC-3 and DC-4

series airplanes) that may be equipped with the ``older'' pneumatic

deicing boot system, the FAA is considering the issuance of

supplemental NPRM's for those airplane models. The purpose of the

supplemental NPRM's would be to require an inspection to determine

which type of pneumatic deicing boots are installed on the airplanes,

and to require operation of the boots at the first sign of ice

accretion if the airplanes have been retrofitted with ``modern'' boots.

Second, for aircraft with ``older'' pneumatic boots installed, the FAA

will continue to investigate other solutions to the unsafe condition of

reduced handling qualities or controllability of the airplane due to

ice accumulations on the protected surfaces. If other solutions are

identified, the FAA may consider further rulemaking.

9. Request To Revise AFM Change

One commenter requests that the proposal to operate the boots at

the first sign of ice accretion be limited to the holding and approach

phases of flight. The commenter states that the Aviation Rulemaking

Advisory Committee (ARAC) Ice Protection Harmonization Working Group

(IPHWG) completed a comprehensive review of past icing accidents/

incidents. The IPHWG concluded that the only phases of flight that

demonstrate a safety concern are holding patterns and various approach

segments; since these operations are conducted at lower airplane speed,

instability could occur as a result of ice accumulations on the wing

and tail surfaces.

The FAA does not concur that the AFM revision should be limited to

the holding and approach phases of flight. The FAA acknowledges that

the IPHWG is working on a proposed operations rule that may only be

applicable during holding and approach phases of flight. However, the

IPHWG continues to work on the proposed rule and has not reached

technical agreement. Since discussions are ongoing, it would not be

appropriate to assume that the IPHWG positions as presented by the

commenter will necessarily be reflected in the actual published

proposal.

Another commenter, an airplane manufacturer, stated that the AFM

for Model SF340A/SAAB340B/SAAB 2000 series airplanes currently does not

limit the operation of the deicing boots during specific phases of

flight. The commenter requests that the AFM change required by

paragraph (a) of the proposal be revised to limit the applicable phases

of flight where the AFM specifies that deicing boots should not be

used. Specifically, the commenter requests that the language be revised

to read ``Deicing boots must not be used during take-off and landing.''

The FAA partially concurs, and acknowledges that clarification is

necessary. It was the FAA's intent that the boots do not have to be

operated at the first sign of ice accretion during those phases of

flight if there are existing procedures in the AFM that prohibit the

operation of the boots during specific phases of flight. However, the

boots must always be operated at the first sign of ice accretion if, in

accordance with the AFM, it is acceptable to operate the boots during

all phases of flight. Therefore, the FAA has revised paragraph (a) of

the final rule to state, ``Except if the AFM otherwise specifies that

deicing boots should not be used for certain phases of flight (e.g.,

take-off, final approach, and landing), compliance with the following

is required.''

With respect to the request to specify that the deicing boots must

not be used during take-off and landing, it would be desirable to

customize the AFM limitation for specific models of airplanes. This

would allow the AFM to clearly indicate to the flightcrew when the

deicing boots should be deactivated, rather than necessitating that the

flightcrew first determine if there are other portions of the AFM that

indicate that the deicing boots should not be used during specific

phases of flight. Therefore, the FAA encourages requests for approval

of alternative methods of compliance to customize the AFM limitation to

the specific airplane model.

However, the FAA does not concur with the request to revise the

final rule that applies to Saab Model SAAB SF340A/SAAB340B/SAAB 2000

series airplanes since the existing Saab AFM does not indicate that the

deicing boots should not be used during take-off and landing. If the

commenter has data to indicate that the deicing boots should not be

used during those phases of flight, the commenter should take action to

revise the AFM and request approval of an alternative method of

compliance.

10. Request To Revise Instructions on When To Deactivate the Boot

System

One commenter requests that two changes be made to paragraph (a) of

the proposal. The first change would be to specify that the wing and

tail leading edge pneumatic deicing boot system may be deactivated only

after completion of an entire deicing cycle after leaving icing

conditions. The commenter also requests that the proposal be revised to

add related procedures for operating speeds, and that related

procedures for operation of the autopilot (if any) be discontinued only

after the airplane is determined to be clear of ice. The commenter

states that natural ice shedding, melting, or sublimation from the

protected areas will mostly eliminate residual ice.

Regarding the commenter's first request, the FAA concurs. For the

reasons the commenter stated, the FAA has revised paragraph (a) of the

final rule from: ``The wing and tail leading edge pneumatic deicing

boot system may be deactivated only after leaving icing conditions and

after the airplane is determined to be clear of ice;'' to ``The wing

and tail leading edge pneumatic deicing boot system may be deactivated

only after completion of an entire deicing cycle after leaving icing

conditions.''

Regarding the commenter's second request, the FAA considers that,

since the suggested change would alter the actions currently required

by this AD, additional rulemaking would be required. The FAA finds that

to delay this action would be inappropriate in light of the identified

unsafe condition. However, the FAA is considering additional rulemaking

concerning operating speeds during icing conditions.

[[Page 63597]]

11. Requests the FAA Consider the Pilot Workload

One commenter states that the proposal would require the pilot to

monitor ice formation and to activate the deicing system almost

constantly. Another commenter suggests that such increase of the

pilot's workload could, of itself, cause an indirect adverse impact on

operational safety. The commenters request that the FAA consider the

additional pilot workload if the proposal is adopted.

The FAA has previously considered the effects on the pilot of

requiring that the deicing boots be activated at the first sign of ice

formation anywhere on the airplane, or upon annunciation from an ice

detector system. The FAA acknowledges that current procedures

recommending activation of the deicing boots at a specific ice

accretion thickness require the flightcrew to closely monitor the ice

accretion. However, since a number of airplanes affected by this AD are

equipped with deicing boot systems with automatic operating modes,

operating the deicing boots at the first sign of ice accretion in an

appropriate automatic mode will favorably influence flightcrew

workload. For airplanes not equipped with automatic deicing boot

operating modes, periodic operation of the boots can be accomplished

based on time intervals consistent with existing icing conditions. The

FAA considers that periodic operation of the boots is not a greater

workload burden than closely monitoring the ice accretion thickness.

For the reasons stated, the FAA has determined that it is

unnecessary to revise the final rule.

12. Request To Withdraw the Proposal: Provide Training Instead

Several commenters request that the FAA withdraw the proposal and

ensure that appropriate information and training regarding the use of

the boots is provided to pilots. The commenters also suggest that a

testing program be accomplished by industry. The commenters assert that

such training, along with an analysis of the testing program, would

eliminate the need for requiring that the deicing boots be activated in

accordance with the proposal. One commenter also adds that the AFM

should only be changed to add a warning that delayed activation of the

pneumatic boot system may be unsafe. Another commenter adds that the

language of the proposed AFM revision may conflict with current AFM

procedures and could confuse operators.

The FAA does not concur that substituting mandatory training for

issuance of an AD is appropriate in this case. The FAA acknowledges

that, in addition to the issuance of an AD, information specified in

the revision to the AFM should be integrated into the pilot training

syllabus. However, the development and use of advisory materials and

training alone are not adequate to address the unsafe condition. The

only method of ensuring that certain information is available to, and

mandatory for, the pilot is through incorporation of the information

into the Limitations Section of the AFM. The appropriate vehicle for

requiring such revision of the AFM is issuance of an AD. No change is

necessary to the final rule in this regard.

13. Request To Consider Procedures Already in Normal Procedures Section

One commenter requests concurrence that procedures existing in the

Normal Procedures section of the AFM be considered as compliant with

the requirements of the proposed AD.

The FAA does not concur that procedures specified in the Normal

Procedures section of the AFM are an equivalent method of compliance

with the AD. The FAA considers that, since the Limitations section of

the AFM is the only section of the AFM that is mandatory [part 91.9 of

the Federal Aviation Regulations (14 CFR 91.9)], the subject required

revision to the AFM must be included in the Limitations section. No

change is necessary to the final rule in this regard.

14. Request To Limit the AD to Only Those Operations Conducive to Icing

Two commenters request that the AFM limitation specified in

paragraph (a) of the proposal be limited to those conditions where

operations conducive to icing exist. The commenters provide examples of

conditions where operations not conducive to icing may exist such as

Hawaii; the Caribbean; short, low altitude flights in the summer; etc.

One of these commenters states that, ``under the proposal, dispatch

with an inoperative boot would be considered prohibited even though the

deicing would never be needed.''

The FAA does not concur that revision of the AD is necessary in

this regard. Paragraph (a) of the AD specifically states that wing and

tail leading edge pneumatic deicing boot systems must be activated at

the first sign of ice formation anywhere on the aircraft, or upon

annunciation from an ice detector system, whichever occurs first. The

FAA considers that, regardless of what geographic area an airplane may

be flying in or what season of the year it may be, the boot system must

be activated if those specified conditions occur.

Regarding dispatch with an inoperative boot, current Master Minimum

Equipment List (MMEL) procedures prohibit dispatch of the airplane into

known or forecast icing conditions if the deicing boots are

inoperative. In the event that icing conditions are inadvertently

encountered during operation in accordance with MMEL provisions,

procedures exist to instruct the flightcrew to exit the icing

conditions immediately. The FAA considers that those existing

procedures will prevent conflict between the requirements of this AD

and perceived problems regarding dispatch with inoperative boots. No

change is necessary to the final rule in this regard.

15. Request To Consider Differences in Airplanes Systems

One commenter requests that the AFM revision specified in paragraph

(a) of the proposed rule be revised for those airplanes that are

equipped with icing detection systems. Such a revision should read

``activate the wing and tail leading edge pneumatic deicing boot system

upon annunciation from an ice detector,'' rather than ``at the first

sign of ice anywhere on the aircraft, or upon annunciation from an ice

detector system, whichever occurs first.'' The commenter states that,

since the sensor for the ice detection system detects ice buildup at

the boot, it would make sense for airplanes that have an ice detection

system to activate the boot only when ice is detected at the boot by

the ice detection system. The commenter further points out that

activating the boot when ice is not forming on the boot will not remove

the ice formations elsewhere on the airplane, but will simply

deteriorate the condition of the boot and provide no safety benefit.

Additionally, the commenter adds that if the ice detection system were

inoperative for dispatch, it would be appropriate as a Master Minimum

Equipment List (MMEL) condition to activate the boot at the first sign

of icing.

The FAA does not concur that the final rule should be revised to

address procedures specifically for airplanes equipped with icing

detection systems. Visual detection of icing by the flightcrew has been

certificated as the primary means of ice detection. Therefore, the FAA

has determined that, although ice detection systems may alert the

flightcrew to the presence of icing, the flightcrew is still

responsible to monitor the airframe for ice accretion.

[[Page 63598]]

No change is necessary to the final rule in this regard. However, in

the event a turbopropeller airplane equipped with pneumatic deicing

boots was also equipped with an ice detection system that was approved

as the primary ice detection system, the operator could request an

alternative method of compliance in accordance with paragraph (b) of

the final rule.

16. Request To Require Additional Operational Procedures

Several commenters propose that the FAA consider that minimum speed

restrictions be used in conjunction with the early activation of the

deicing boots. Some of the commenters specify that these speed

additions be applied during landing approach. One of the commenters

expresses concern that various reports and research indicate that

increasing the angle-of attack with even a small ice formation on the

airfoil can cause large increases in drag and loss of lift. The

commenter contends that control of the angle-of-attack is critical in

maintaining airfoil performance, and concludes that additional

operational procedures must be added.

The FAA concurs that certain operational procedures may be

beneficial when used with early activation of the deicing boots. As a

complement to this AD, the FAA is considering rulemaking regarding

minimum speeds in icing conditions. As mentioned previously, the FAA

encourages manufacturers to present data via a request for approval of

an alternative method of compliance to substantiate that their

airplanes are either capable of flying safely with ice that accumulates

prior to boot activation, or that they are not capable of flying safely

but there are other means to address the unsafe condition. For example,

in the case of Cessna Model 560 series airplanes, the stall warning

margins were modified to ensure the airplane could safely operate with

ice accretions on the protected surfaces. No change is necessary to the

final rule in this regard.

17. Request To Mandate Installation of an Ice Detection System

One commenter suggests that a required installation of a reliable

ice detection system might alleviate the difficulties associated with

flightcrew recognition of airfoil ice accretions. The commenter notes

that, historically, the problem of ice detection has been the ability

of the flightcrew to either identify that the airfoil has ice adhering

to it or accurately determine that a certain thickness of ice exists on

the airfoil prior to activation of the boot system.

The FAA concurs that installation of a reliable ice detection

system would alleviate the difficulties associated with flightcrew

recognition of airfoil ice accretions. This issue is being addressed by

an ARAC working group. Upon receipt of a recommendation from ARAC, the

FAA may consider further rulemaking. In the interim, the FAA is issuing

these airworthiness directives to impose a relatively simple deicing

boot operational change to address the reduced handling qualities or

controllability of the airplane due to ice accumulations on the

protected surfaces. No change is necessary to the final rule in this

regard.

18. Request To Require Action To Reduce Adhesion Characteristics

One commenter requests that action be taken to minimize or reduce

the ice adhesion characteristics of boot material. The commenter

asserts that one reason flightcrews may be seeing large amounts of

residual ice may be that, as the boot ages, the tendency for residual

ice to stick to the boot surface may increase if the adhesion qualities

of the boot materials are not properly maintained. In addition, the

commenter suggests that the use of certain compounds (e.g., ICEX, an

ice-phobic chemical spray) can reduce ice adhesion by substantial

margins.

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

rulemaking to reduce adhesion characteristics of boot material. The FAA

considers that normal wear and tear on the deicing boot materials is to

be expected, and the adhesion characteristics of the boot increases as

the boot surface degrades over time. Operators have the responsibility

to monitor the performance of the deicing boots installed on their

airplanes, and to perform maintenance as required.

The FAA acknowledges that use of certain ice-phobic chemicals may

provide an additional safety benefit. However, a variety of factors

(e.g., normal wear and tear, ``patching,'' and oxidation of boot

material) exist in varying degrees on individual airplanes. As a

result, the optimum frequency of application will vary during the life

of the boot. The FAA has received no quantitative data to demonstrate

the adequacy of particular amounts of ice phobic chemical sprays or to

provide adequate intervals of application. Therefore, the FAA cannot

establish an appropriate application interval at this time. However, if

additional data becomes available, the FAA may consider further

rulemaking.

19. Request To Consider the Associated Maintenance Procedures and

Increased Costs

Several commenters point out that certain maintenance requirements

should be considered if the proposed AFM revision is required. One

commenter notes that a detailed review of maintenance procedures should

be conducted regarding the deicing boots to ensure that, as the boot

ages, the boot system continues to effectively shed ice.

Several commenters request that the FAA also consider the

additional costs that the proposed AFM revision would require. One

commenter states that the added cycling of the boots will require

additional maintenance. The commenters express concern that the boots

will wear out faster, need to be replaced at an accelerated rate, and

thereby add additional costs.

The FAA acknowledges the concerns of these commenters. The FAA

considered the deicing boot fatigue issues surrounding the proposed AD,

such as the reliability of the deicing boots. Reliability of the

deicing boots is affected by several factors, including: maintenance

practices; abrasion during dry air, rain, hail, snow, and icing

operations; oxidation; and, fatigue resulting from boot cycling.

However, none of the commenters provided cost estimates for any of

the maintenance costs or replacement costs. The FAA did receive certain

other information from a large operator of two airplane models that

will be affected by this final rule. (One of the airplane models in

that fleet currently observes the early-activation procedures required

by this final rule and the other airplane model does not.) The operator

stated that the largest contributor to periodic replacement of deicing

boots on the fleet was erosion of the boot surface, rather than fatigue

that would be caused by activation of deicing boots at the first sign

of ice accretion.

The FAA recognizes that, in accomplishing the requirements of any

AD, operators may incur ``incidental'' 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 does not include incidental costs. In the case of this AD,

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:

for some operators, implementation may necessitate extensive retraining

among their flightcrews; for others, implementation

[[Page 63599]]

may merely be considered a typical part of the routine, continuous

training of their flightcrews. In light of this, it would be nearly

impossible for the FAA to calculate accurately or to reflect all costs

associated with the AFM revision required by this AD. The FAA has

determined that direct and incidental costs are still outweighed by the

safety benefits of the AD.

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 described

previously. 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

There are approximately 426 Model F-27 and FH-227 series airplanes

of the affected design in the worldwide fleet. The FAA estimates that

47 airplanes of U.S. registry will be affected by this AD.

It will take approximately 1 work hour per airplane to accomplish

the required AFM revisions, at the average labor rate of $60 per work

hour. Based on these figures, the cost impact of the AD on U.S.

operators is estimated to be $2,820, or $60 per airplane.

The cost impact figure discussed above is based on assumptions that

no operator has yet accomplished any of the requirements of this AD

action, and that no operator would accomplish those actions in the

future if this AD were not adopted.

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 final evaluation has been prepared for this action

and it is contained in the Rules Docket. A copy of it may be obtained

from the Rules Docket at the location provided under the caption

ADDRESSES.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, 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 U.S.C. 106(g), 40113, 44701.

Sec. 39.13 [Amended]

2. Section 39.13 is amended by adding the following new

airworthiness directive:

99-19-09 Maryland Air Industries, Inc.: Amendment 39-11298. Docket

99-NM-143-AD.

Applicability: Model F-27 and FH-227 series airplanes equipped

with pneumatic deicing boots, certificated in any category.

Compliance: Required as indicated, unless accomplished

previously.

To ensure that flightcrews activate the wing and tail pneumatic

deicing boots at the first signs of ice accumulation on the

airplane, accomplish the following:

(a) Within 10 days after the effective date of this AD: Revise

the Limitations Section of the FAA-approved Airplane Flight Manual

(AFM) to include the following requirements for activation of the

ice protection systems. This may be accomplished by inserting a copy

of this AD in the AFM.

`` Except if the AFM otherwise specifies that deicing boots

should not be used for certain phases of flight (e.g., take-off,

final approach, and landing), compliance with the following is

required.

Wing and Tail Leading Edge Pneumatic Deicing Boot System,

if installed, must be activated:

--At the first sign of ice formation anywhere on the aircraft,

or upon annunciation from an ice detector system, whichever occurs

first; and

--The system must either be continued to be operated in the

automatic cycling mode, if available; or the system must be manually

cycled as needed to minimize the ice accretions on the airframe.

``The wing and tail leading edge pneumatic deicing boot

system may be deactivated only after completion of an entire deicing

cycle after leaving icing conditions.''

(b) 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, New York Aircraft Certification

Office, FAA, Engine and Propeller Directorate. The request shall be

forwarded through an appropriate FAA Operations Inspector, who may

add comments and then send it to the Manager, New York ACO.

Note 1: Information concerning the existence of approved

alternative methods of compliance with this AD, if any, may be

obtained from the New York ACO.

(c) Special flight permits may be issued in accordance with

Secs. 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) This amendment becomes effective on December 27, 1999.

Issued in Renton, Washington, on November 10, 1999.

John J. Hickey,

Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 99-30135 Filed 11-19-99; 8:45 am]

BILLING CODE 4910-13-U