Airworthiness Standards; Rain and Hail Ingestion Standards

SUMMARY: This document proposes changes to the water and hail ingestion

standards for aircraft turbine engines. This proposal addresses engine

power-loss and instability phenomena attributed to operation in extreme

rain or hail that are not adequately addressed by current requirements.

This proposal also harmonizes these standards with rain and hail

ingestion standards being amended by the Joint Aviation Authorities

(JAA). The proposed changes, if adopted, would establish one set of

common requirements, thereby reducing the regulatory hardship on the

United States and worldwide aviation industry, by eliminating the need

for manufactures to comply with different sets of standards when

seeking type certification from the Federal Aviation Administration

(FAA) and JAA.

DATES: Comments to be submitted on or before November 7, 1996.

ADDRESSES: Comments on this notice may be delivered or mailed, in

triplicate, to: Federal Aviation Administration, Office of the Chief

Counsel, Attention: Rules Docket (AGC-200), Docket No. 28652, Room

915G, 800 Independence Avenue, SW., Washington, DC 20591. Comments

submitted must be marked: ``Docket No. 28652. Comments may also be sent

electronically to the following Room 915G on weekdays, except Federal

holidays, between 8:30 a.m. and 5:00 p.m.

FOR FURTHER INFORMATION CONTACT: Thomas Boudreau, Engine and Propeller

Standards Staff, ANE-110, Engine and Propeller Directorate, Aircraft

Certification Service, FAA, New England Region, 12 New England

Executive Park, Burlington, Massachusetts 01803-5229; telephone (617)

238-7117; fax (617) 238-7199.

SUPPLEMENTARY INFORMATION:

Comments Invited

Interested persons are invited to participate in the making of the

proposed rule by submitting such written data, views, or arguments as

they may desire. Comments relating to the environmental, energy,

federalism, or economic impact that might result from adopting the

proposals in this notice are also invited. Substantive comments should

be accompanied by cost estimates. Comments must identify the regulatory

docket or notice number and be submitted in triplicate to the Rules

Docket address specified above.

All comments received, as well as a report summarizing each

substantive public contact with FAA personnel on this rulemaking, will

be filed in the docket. The docket is available for public inspection

before and after the comment closing date.

All comments received on or before the closing date will be

considered by the Administrator before taking action on this proposed

rulemaking. Late-filed comments will be considered to the extent

practicable. The proposals contained in this notice may be changed in

light of comments received.

Commenters wishing the FAA to acknowledge receipt of their comments

submitted in response to this notice must include a pre-addressed,

stamped postcard on those comments on which the following statement is

made: ``Comments to Docket No. 28652.'' The postcard will be date

stamped and mailed to the commenter.

Availability of NPRMs

An electronic copy of this document may be downloaded using a modem

and suitable communications software from the FAA regulations section

of the Fedworld electronic bulletin board service (telephone: 703-321-

3339), the Federal Register's electronic bulletin board service

(telephone: 202-512-1661), or the FAA's Aviation Rulemaking Advisory

Committee Bulletin Board service (telephone: 202-267-5948).

Internet users may reach the FAA's web page at http://www.faa.gov

or the Federal Register's webpage at http://www.access.gpo.gov/su__docs

for access to recently published rulemaking documents.

Any person may obtain a copy of this NPRM by submitting a request

to the Federal Aviation Administration, Office of Rulemaking, ARM-1,

800 Independence Avenue, SW., Washington, DC 20591, or by calling (202)

267-9680. Communications must identify the notice number of this NPRM.

Person interested in being placed on the mailing list for future

NPRM's should request from the above office a copy of Advisory Circular

No. 11-2A, Notice of Proposed Rulemaking Distribution System, that

describes the application procedure.

Background

Statement of the Problem

There have been a number of multiple turbine engine power-loss and

instability events, forced landings, and accidents attributed to

operating airplanes in extreme rain or hail. Investigations have

revealed that ambient rain or hail concentrations can be amplified

significantly through the turbine engine core at high flight speeds and

low engine power conditions. Rain or hail through the turbine engine

core may degrade compressor stability, combustor flameout margin, and

fuel control run down margin. Ingestion of extreme quantities of rain

or hail through the engine core may ultimately produce a number of

engine anomalies, including surging, power loss, and engine flameout.

Industry Study

In 1987 the Aerospace Industries Association (AIA) initiated a

study of natural icing effects on high bypass ratio (HBR) turbofan

engines that concentrated primarily on the mechanical damage aspects of

icing encounters. It was discovered during that study that separate

power-loss and instability phenomena existed that were not related to

mechanical damage. consequently, in 1988 another AIA study was

initiated to determine the magnitude of these threats and to recommend

changes to part 33, if appropriate. AIA, working with the Association

Europeenne des Constructeurs de Materiel Aerospatial (AECMA), concluded

that a potential flight safety threat exists for turbine engines

installed on airplanes operating in extreme rain and hail. Further, the

study concluded that the current water and hail ingestion standards of

14 CFR part 33 do not adequately address this threat.

Engine Harmonization Effort

the FAA is committed to undertaking and supporting harmonization of

standards in part 33 with those in Joint Aviation Requirements-Engines

(JAR-E). In August 1989, as a result of that commitment, the FAA Engine

and propeller Directorate participated in a meeting with the Joint

Aviation Authorities (JAA), AIA, and AECMA. The purpose of the meeting

was to establish a philosophy, guidelines, and a working relationship

regarding the resolution of issues arising from standards that need

harmonization, including the adoption of new standards

[[Page 41689]]

when needed. All parties agreed to work in partnership to address

jointly the harmonization task. The partnership was later expanded to

include the airworthiness authority of Canada, Transport Canada.

This partnership identified seven items which where considered the

most critical to the initial harmonization effort. New rain and hail

ingestion standards are an item on this list of seven items and,

therefore, represent a critical harmonization effort.

Aviation Rulemaking Advisory Committee Project

In December 1992, the FAA requested the Aviation Rulemaking

Advisory Committee (ARAC) to evaluate the need for new rain and hail

ingestion standards. This task, in turn, was assigned to the Engine

Harmonization Working Group (EHWG) of the Transport Airplane and Engine

Issues Group (TAEIG) on December 11, 1992 (57 FR 58840). On November 7,

1995, the TAEIG recommended to the FAA that it proceed with rulemaking

and associated advisory material even though one manufacturer has

expressed reservations. This NPRM and associated advisory material

reflects the ARAC recommendations.

Disposition of Objections

One manufacturer participating in the EHWG has expressed

reservations with the proposal. The reservations focused on the degree

of conservatism built into the assumptions regarding weather

statistics. These reservations include concerns about a bias in the

hail characterization towards geographical areas of extremely high

hailstorm probabilities and with an apparent rounding up of the hail

threat definition from 8/3 g/m\3\ to 10 g/m\3\. The manufacturer also

expressed concern regarding the lack of standardized test procedures

and analytical methods for compliance within the industry.

During the early phase of defining the environmental threat, for

both rain and hail, engineering judgment suggested that expressing rain

water content (RWC) and hail water content (HWC) as a function of a

joint probability was an appropriate method. That joint probability is

the product of the prior probability of a storm occurring at a given

point and the conditional probability of a given water concentration

value occurring within that storm. Given the potential for a pilot to

avoid a storm and the ability for an engine to recover sufficiently for

continued safe flight, a joint probability of 10-\8\ was

determined adequate for establishing the certification standards for

rain and hail. Accounting for hail shaft exposure times, the hail

threat levels could vary from 8.7 g/m\3\ to 10.2 g/m\3\. The choice of

10 g/m\3\ was agreed to by the EHWG as the certification standard that

would be suitable for all applications. It was not simply a round up.

Admittedly, the only credible hail data available was for high hail

probability areas in North America and Europe. While these data may not

represent the average world environment, they do represent areas of

high commercial air traffic through which aircraft equipped with

turbine engines normally operate.

The EHWG also consider the proposal and the associated

harmonization activity to be an effective method of reaching a more

uniform method for compliance by manufacturers. That activity has

already fostered a significant sharing of knowledge on the subject.

Current Requirements

The current water and large hailstone ingestion standards are valid

tests for addressing permanent mechanical damage resulting from such

ingestions. However, they do not adequately address engine power-loss

and instability effects, such as run down and flameout at lower than

takeoff-rated power settings for turbine engines installed on

airplanes.

The EHWG concluded that, with respect to power-loss and instability

effects, the current water ingestion standard is adequate for turbine

engines installed on rotorcraft (turboshaft engines) as an alternative

to the new rain and hail ingestion standards. The EHWG reached this

conclusion after it had reviewed the service experience of rotorcraft

turbine engines and could not find an inservice event that would

indicate that the current water ingestion standard are inadequate for

that application. There are differences between rotorcraft and

airplanes that help to explain the differences in the service

experience of rotorcraft turbine engines versus other turbine engines.

Rotorcraft turbine engines operate at higher power settings during

descent than turbine engines installed on airplanes. Also, rotorcraft

operate at lower flight speeds than airplanes. The combination of

higher engine power and lower flight speed significantly reduces the

water concentration amplification effects on rotorcraft turbine

engines. Therefore, the proposed new rain and hail ingestion standards

apply to all turbine engines, while a harmonized version of a four

percent water to engine airflow by weight ingestion standard is

proposed as an alternative for turbine engines installed on rotorcraft.

General Discussion of the Proposals

Section 23.901(d)(2), Sec. 23.903(a)(2) and Sec. 25.903(a)(2)

The proposed amendments would revise Sec. 23.903(a)(2) and

Sec. 25.903(a)(2) to be consistent with the proposed part 33 changes.

Additionally, proposed Sec. 23.901(d)(2) would replace the current text

with new text requiring each turbine engine installation to be

constructed and arranged not to jeopardize compliance of the engine

with Sec. 23.903(a)(2). This would ensure that the installed engine

retains the acceptable rain, hail, ice, and bird ingestion capabilities

established for the uninstalled engine under Sec. 23.903(a)(2).

Section 33.77

The proposed amendments would remove the large hailstone ingestion

standards now specified in Sec. 33.77 (c) and (e), and place them in

new Sec. 33.78 (a)(1) and (c). The proposal would also harmonize the

four percent water to engine airflow by weight ingestion standard,

currently specified in Sec. 33.77 (c) and (e), and place it in new

Sec. 33.78(b) as an alternative standard for rotorcraft turbine engines

to the proposed new rain and hail ingestion standards. New water and

hail ingestion standards for all turbine engines would be introduced in

new Sec. 33.78(a)(2). All rain and hail ingestion standards would then

be found in one section, as in the current JAR-E.

The intent of the current water ingestion standard is to address a

number of concerns including power-loss, instability, and the potential

hazardous effects of water associated with case contraction. As stated

previously, there have been numerous power-loss and instability events

on airplane turbine engines since the standard was promulgated (39 FR

35463, October 1, 1974). The need to better address power-loss and

instability effects at lower than takeoff-rated power settings led to

the proposed new standards for all turbine engines (new

Sec. 33.78(a)(2)). Collectively, the proposed new standards and the

proposed changes as contained in new Sec. 33.78 (a)(2) and (b) also

better address potential concerns associated with case contractions on

turbine engines since they are based on a more thorough understanding

of the in-flight effects of rain and hail ingestion.

Section 33.78

The proposed Sec. 33.78 would consolidate all harmonized rain and

hail

[[Page 41690]]

ingestion standards for turbine engines, and the corresponding

harmonized acceptance criteria, into a single section. The proposal

also introduces new rain and hail ingestion standards for turbine

engines to address the power-loss and instability phenomena identified

by AIA and AECMA.

Currently, part 33 and JAR-E have different acceptance criteria for

the water and large hailstone ingestion standards. In general, part 33

does not permit any sustained power or thrust loss after the ingestion,

while JAR-E permits some power or thrust loss and some minimal amount

of mechanical damage. The EHWG determined, however, that the current

FAA post ingestion power loss criterion does not consider thrust and

power loss variabilities, such as inherent measurement inaccuracies.

Therefore, allowing some measured power or thrust loss would be

reasonable but must not reduce the level of safety intended by these

requirements.

The EHWG concluded that sufficient airplane performance margins

exist to permit sustained post ingestion power or thrust losses up to 3

percent at any value of the power or thrust setting parameter.

Variabilities and uncertainties associated with thrust and power

measurements could conceivably result in upwards of a 3 percent power

or thrust measurement error. Therefore, measured post ingestion power

or thrust losses up to 3 percent are acceptable and do not represent a

reduction in the level of safety provided by current FAA water and

large hailstone ingestion standards. However, measured post ingestion

power or thrust losses greater than 3 percent, at any value of the

primary power or thrust setting parameter, can only be accepted when

supported by appropriate airplane performance assessments.

The EHWG also discussed levels of acceptable engine performance

degradation that might be experienced as a result of certification

testing. This degradation is a power or thrust reduction when pre-test

and post test comparisons are made at any given values of the engine

manufacturer's normal performance parameters other than the primary

power or thrust setting parameter. This power or thrust degradation

must not affect the measured power or thrust of the engine at any value

of the primary power or thrust setting parameters, but would tend to

reduce the available gas path temperature margin of the engine after

the test. It is the judgment of the EHWG, based on certification and

development test experience, that current and future technology engines

should be capable of demonstrating less than 10 percent engine

performance degradation from a single hail or rain ingestion event.

Some members of the EHWG believe that values greater than 10 percent

can be safely accommodated, but consensus could not be obtained in

defining this uppermost value. The EHWG accepted the 10 percent value

as a compromise certification standard for future use in the context of

rain and hail ingestion testing. In the event that future certification

tests result in engine performance degradations that exceed 10 percent,

the actual demonstrated level must be evaluated for acceptability

against the criterion of aircraft safety.

The proposed new rain and hail ingestion standards to address the

power loss and instability phenomena refer to a proposed new FAR part

33 appendix for a definition of maximum concentrations of rain and hail

in the atmosphere. It is expected that a combination of tests and

analyses would be needed to demonstrate compliance. Therefore, this

proposal allows for various means of compliance.

Allowing various means of compliance has distinct advantages. The

variables associated with an ingestion event are best addressed through

a combination of tests and analyses. Also, it is anticipated that

further insight into the phenomenon of rain and hail ingestion would be

gained through the development of these various compliance methods.

Finally, the EHWG believes that applicants would develop compliance

methods which minimize the cost impact.

Rain and hail ingestion standards embodied in this rule represent

an extremely remote probability of encounter (1 x 10 -8). They are

based on current assessments of atmospheric and meteorological

conditions and aircraft engine service experience. Both the FAA and the

JAA agree that the need for revised standards should be considered as

additional service and atmospheric data warrant.

Appendix B

Proposed Appendix B defines the certification standard atmospheric

concentrations of rain and hail. These values were derived through

detailed meteorological surveys and statistical analyses and represent

an extremely remote aircraft encounter.

Paperwork Reduction Act

In accordance with the Paperwork Reduction Act of 1990 (44 U.S.C.

3501 et seq.), there are no requirements for information collection

associated with this proposed rule.

International Compatibility

The FAA has reviewed corresponding International Civil Aviation

Organization international standards and recommended practices and

Joint Aviation Authorities requirements and has identified no

difference in these proposed amendments and the foreign regulations.

Regulatory Evaluation Summary

Proposed changes to Federal regulations must undergo several

economic analyses. First, Executive Order 12866 directs that each

Federal agency shall propose or adopt a regulation only upon a reasoned

determination that the benefits of the intended regulation justify its

costs. Second, the Regulatory Flexibility Act of 1980 requires agencies

to analyze the economic effect of regulatory changes on small entities.

Third, the Office of Management and Budget directs agencies to assess

the effects of regulatory changes on international trade. In conducting

these analyses, the FAA has determined that this rule: (1) Would

generate benefits that justify its costs and is not a ``significant

regulatory action'' as defined in the Executive Order; (2) is not

significant as defined in DOT's Regulatory Policies and Procedures; (3)

would not have a significant impact on a substantial number of small

entities; and (4) would not constitute a barrier to international

trade. These analyses, available in the docket, are summarized below.

Incremental Certification Costs

The proposed rule would permit a range of compliance options,

thereby enabling manufacturers to select cost-minimizing approaches.

Approaches that maximize the use of analytical methods would most

likely be the least expensive means to demonstrate compliance, while

approaches that rely primarily on engine testing in a simulated rain

and hail environment would likely be the most costly. Incremental cost

estimates supplied by industry varied depending on engine model and the

testing method used.

FAA conservatively estimates that incremental certification costs

for airplane turbine engines would be approximately $667,000; this

includes $300,000 in additional engineering hours, and $367,000 for the

prorated share of the cost of a test facility.

Incremental Manufacturing and Operating Costs

Predicting the rule's effect on manufacturing costs is complicated

by design/cost tradeoffs, the large number of permutations of

modifications that

[[Page 41691]]

could achieve the desired result, and because engine design takes place

in the context of constant technological change. Based on discussions

with industry representatives, the FAA expects that, once rain/hail

centrifuging and engine cycle models are established, compliance would

be accomplished through design modifications that would have little

impact on manufacturing costs. Such design features may affect: (1) fan

blade/propeller, (2) spinner/nose cone, (3) bypass splitter, (4) engine

bleeds, (5) accessory loads, (6) variable stator scheduling, and (7)

fuel control. Similarly, the FAA expects that the rule would have a

negligible effect on operating costs (again, based on discussions with

industry representatives).

Expected Benefits

Rain or hail related in-flight engine shutdowns are rare

occurrences. This is due, in large part, to the high quality of

meteorological data available to ground controllers and pilots, and to

well established weather avoidance procedures. However, while such

events are infrequent, they pose a serious hazard because they

typically occur during a critical phase of flight where recovery is

difficult or impossible.

An examination of FAA and National Transportation Safety Board

(NTSB) records revealed two accidents that were the result of inflight

engine shutdowns or rundowns caused by excessive water ingestion. In

each case, the aircraft was in the descent phase of flight. These

accidents form the basis of the expected benefits of the proposed rule,

as summarized below. However, the following summary should be

considered a conservative estimate of the rule's potential benefits for

three reasons.

First, the rule should have the effect of increasing turbine engine

water ingestion tolerance regardless of the source of water. The

historical record shows that many accidents (not included in the

following benefit estimates) were caused by other forms of water such

as snow and graupel. It is possible that the aircraft in some of these

cases would have benefited from the proposed rule.

Second, several other incidents, while not resulting in a crash,

nevertheless had catastrophic potential. This potential could be

exacerbated by the development of more efficient turbofan powerplants

which have permitted large aircraft designs incorporating fewer

engines. An industry study identified seven events (not recorded in

either the FAA or NTSB databases) in which rain and/or hail affected

two or more engines and resulted in an inflight shutdown of at least

one engine.

Third, heavy rain and hail are often accompanied by severe

turbulence and windshear. While recovery from a water induced engine

shutdown is frequently successful, the ability to maintain engine power

during an encounter with an unexpected downdraft could be crucial to

avoiding a crash.

Benefits of Prevented Aircraft Damage

The available accident and aircraft usage data suggest the

categories that are used to classify the benefits of the proposed rule.

These classifications are: (1) Large air carrier aircraft (major and

national air carriers), and (2) other air carrier aircraft (large

regional, medium regional, commuter, and other small certificated air

carriers).

An examination of accident records for the period 1975-90,

indicates that, in the absence of the proposed rule, the probability of

a hull loss due to a water induced loss of engine power is 0.0104 per

million airplane departures for large air carriers, and 0.0276 per

million airplane departures for other air carriers.

The calculation of the rule's benefits, then, depends on the degree

to which the rule can reduce this risk. According to industry

representatives, compliance with the proposed standards would reduce

the accident rate by two orders of magnitude. That is, the rule is

expected to be 99 percent effective in reducing water ingestion

accidents. FAA estimates that the annual average benefits per airplane

from prevented aircraft damage would be approximately $337 and $97 for

large air carriers and other air carriers, respectively.

Benefits of Prevent Injuries and Fatalities

Using projections from the FAA Aviation Forecast, this analysis

assumes that the average large air carrier airplane has 168 seats and a

load factor of 61 percent. The average regional airplane is assumed to

have 30 seats and a load factor of 51 percent. The estimated

distribution of fatal, serious, and minor injuries is derived from the

actual distribution of casualties in the accidents cited above. On the

basis of these assumptions, FAA estimates the annual benefits of

prevented casualties per airplane would be $3,062 for operations by

large air carriers and $706 for operations by other air carriers.

Benefit-Cost Analysis

The benefits and costs of the proposed rule are compared for two

representative engine certifications using the following assumptions:

(1) For each certification, 50 engines are produced per year for 10

years (500 engines), (2) incremental certification costs are incurred

in year ``0'', (3) engine production begins in year ``3'', (4) the

first engines enter service in year ``4'', (5) each engine is retired

after 10 years, (6) the discount rate is 7 percent. Also, in order to

compare incremental engine costs with expected benefits (which are

expressed in terms of the reduction in the airplane accident rate) this

analysis assumes that each airplane has two engines.

For each airplane/engine type, the annual benefit per aircraft is

the sum of the expected property and casualty benefits. The total

benefit for each type certification, then, is the product of the per

aircraft annual benefit and the number of aircraft in service summed

over the life of the engines. Thus, for representative type

certifications, discounted lifecycle benefits would be approximately

$3.7 million and $0.8 million for operations by large air carriers and

other air carriers, respectively.

FAA finds that the rule would be cost-beneficial. Under

conservative production, service life, and incremental engine

certification cost assumptions, the expected discounted benefits of

prevented casualties and aircraft damage would exceed discounted costs

by a factor ranging from 5.5 ($3,661,084/$667,000) for operations by

large air carriers to 1.3 ($864,696/$667,000) for operations by other

air carriers.

Harmonization Benefits

In addition to the benefits of increased safety, the rule

harmonizes with JAR requirements, thus reducing costs associated with

certificating aircraft turbine engines to differing airworthiness

standards.

Regulatory Flexibility Determination

The Regulatory Flexibility Act (RFA) of 1980 was enacted by

Congress to ensure that small entities are not unnecessarily or

disproportionately burdened by Government regulations. The RFA requires

a Regulatory Flexibility Analysis if a rule is expected to have a

``significant economic impact on a substantial number of small

entities.'' Based on the standards and thresholds specified in

implementing FAA Order 2100.14A, Regulatory Flexibility Criteria and

Guidance, the FAA has determined that the rule would not have a

significant impact on a substantial number of small manufacturers or

operators because no turbine engine manufacturer is a ``small entity''

as defined in the order.

[[Page 41692]]

International Trade Impact Assessment

The rule would have little or no effect on trade for either U.S.

firms marketing turbine engines in foreign markets or foreign firms

marketing turbine engines in the U.S.

Federalism Implications

The regulations proposed herein would 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

proposal would not have sufficient federalism implications to warrant

the preparation of a Federalism Assessment.

Conclusion

For the reasons discussed above, including the findings in the

Regulatory Flexibility Determination and the International Trade Impact

Analysis, the FAA has determined that this proposed regulation is not

significant under Executive Order 12866. In addition, the FAA certifies

that this proposal, if adopted, would not have a significant economic

impact, positive or negative, on a substantial number of small entities

under the criteria of the Regulatory Flexibility Act. This proposal is

not considered significant under DOT Regulatory Policies and Procedures

(44 FR 11034, February 26, 1979). An initial regulatory evaluation of

the proposal, including a Regulatory Flexibility Determination and

Trade Impact Analysis, has been placed in the docket. A copy may be

obtained by contacting the person identified under FOR FURTHER

INFORMATION CONTACT.

List of Subjects in 14 CFR Parts 23, 25, and 33

Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

In consideration of the foregoing, the Federal Aviation

Administration proposes to amend parts 23, 25, and 33 of the Federal

Aviation Regulations (14 CFR part 23, 14 CFR part 25, and 14 CFR part

33) as follows:

PART 23--AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND

COMMUTER CATEGORY AIRPLANES

1. The authority citation for part 23 continues to read as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.

2. Section 23.901 is amended by revising paragraph (d)(2) to read

as follows:

Sec. 23.901 Installation.

* * * * *

(d) * * *

(2) Ensure that the capability of the installed engine to withstand

the ingestion of rain, hail, ice, and birds into the engine inlet is

not less than the capability established for the engine itself under

Sec. 23.903(a)(2).

* * * * *

3. Section 23.903 is amended by revising paragraph (a)(2) to read

as follows:

Sec. 23.903 Engines.

(a) * * *

(2) Each turbine engine must either--

(i) Comply with Sec. 33.77 and Sec. 33.78 of this chapter for an

airplane for which application for type certification is made on or

after [Insert effective date of final rule]; or

(ii) Comply with Sec. 33.77 of this chapter in effect on October

31, 1974, and must have a foreign object ingestion service history that

has not resulted in any unsafe condition for an airplane for which

application for type certification was made before [Insert effective

date of final rule]; or

(iii) Be shown to have a foreign object ingestion service history

in similar installation locations which has not resulted in any unsafe

condition.

Note: Sec. 33.77 of this chapter in effect on October 31, 1974,

was published in 14 CFR parts 1 to 59, Revised as of January 1,

1975. See 39 FR 35467; October 1, 1974.

* * * * *

PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES

4. The authority citation for part 25 continues to read as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.

5. Section 25.903 is amended by revising paragraph (a)(2) to read

as follows:

Sec. 25.903 Engines.

(a) * * *

(2) Each turbine engine must either--

(i) Comply with Sec. 33.77 and Sec. 33.78 of this chapter for an

airplane for which application for type certification is made on or

after [Insert effective date of final rule]; or

(ii) Comply with Sec. 33.77 of this chapter in effect on October

31, 1974, and must have a foreign object ingestion service history that

has not resulted in any unsafe condition for an airplane for which

application for type certification was made before [Insert effective

date of final rule]; or

(iii) Be shown to have a foreign object ingestion service history

in similar installation locations which has not resulted in any unsafe

condition.

Note: Sec. 33.77 of this chapter in effect on October 31, 1974,

was published in 14 CFR parts 1 to 59, Revised as of January 1,

1975. See 39 FR 35467; October 1, 1974.

* * * * *

PART 33--AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES

6. The authority citation for part 33 continues to read as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.

7. Section 33.77 is amended by revising paragraphs (c) and (e) to

read as follows:

Sec. 33.77 Foreign object ingestion.

* * * * *

(c) Ingestion of ice under the conditions prescribed in paragraph

(e) of this section, may not cause a sustained power or thrust loss or

require the engine to be shut down.

* * * * *

(e) Compliance with paragraphs (a), (b), and (c) of this section

must be shown by engine test under the following ingestion conditions:

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

Speed of foreign

Foreign object Test quantity object Engine operation Ingestion

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

Birds:

3-ounce size................ One for each 50 Liftoff speed of Takeoff........... In rapid sequence

square inches of typical aircraft. to simulate a

inlet area, or flock encounter

fraction thereof, and aimed at

up to a maximum selected critical

of 16 birds. areas.

Three-ounce bird

ingestion not

required if a 1\1/

2\-pound bird

will pass the

inlet guide vanes

into the rotor

blades.

[[Page 41693]]

1\1/2\-pound size........... One for the first Initial climb Takeoff........... In rapid sequence

300 square inches speed of typical to simulate a

of inlet area, if aircraft. flock encounter

it can enter the and aimed at

inlet, plus one selected critical

for each areas.

additional 600

square inches of

inlet area, or

fraction, thereof

up to a maximum

of 8 birds.

4-pound size................ One, if it can Maximum climb Maximum cruise.... Aimed at critical

enter the inlet. speed of typical area.

aircraft, if the

engine has inlet

guide vanes.

Liftoff speed of Takeoff........... Aimed at critical

typical aircraft, area.

if the engine

does not have

inlet guide

vanes.

Ice............................. Maximum Sucked in......... Maximum cruise.... To simulate a

accumulation on a continuous

typical inlet maximum icing

cowl and engine encounter at 25

face resulting deg.F.

from a 2-minute

delay in

actuating anti-

icing system, or

a slab of ice

which is

comparable in

weight or

thickness for

that size engine.

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

Note: The term ``inlet area'' as used in this section means the engine inlet projected area at the front face of

the engine. It includes the projected area of any spinner or bullet nose that is provided.

8. Section 33.78 is added to part 33, to read as follows:

Sec. 33.78 Rain and hail ingestion.

(a) All engines. (1) The ingestion of large hailstones (0.8 to 0.9

specific gravity) at the maximum rough air speed, up to 15,000 feet

(4,500 meters), associated with a representative aircraft, with the

engine at maximum continuous power, may not cause unacceptable

mechanical damage or unacceptable power or thrust loss after the

ingestion, or require the engine to be shut down. One-half the number

of hailstones shall be aimed randomly over the inlet face area and the

other half aimed at the critical inlet fact area. The hailstone number

and size shall be determined as follows:

(i) One 1-inch (25 millimeters) diameter hailstone for engines with

inlet area of not more than 100 square inches (0.0645 square meters).

(ii) One 1-inch (25 millimeters) diameter and one 20-inch (50

millimeters) diameter hailstone for each 150 square inches (0.0968

square meters) of inlet area, or fraction thereof, for engines with

inlet area more than 100 square inches (0.0645 square meters).

(2) Except as provided in paragraph (b) of this section, it must be

shown that each engine is capable of acceptable operation throughout

its specified operating envelope when subjected to sudden encounters

with the certification standard concentrations of rain and hail, as

defined in Appendix B to this part. Acceptable engine operation

precludes flameout, run down, continued or non-recoverable surge or

stall, or loss of acceleration and deceleration capability during any

three minute continuous period in rain and during any 30 second

continuous period in hail. It must also be shown after the ingestion

that there is no unacceptable mechanical damage, unacceptable power or

thrust loss, or other adverse engine anomalies.

(b) Engines for rotocraft. As an alternative to the requirements

specified in paragraph (a)(2) of this section, for rotocraft turbine

engines only, it must be shown that each engine is capable of

acceptable operation during and after the ingestion of rain with an

overall ratio of water droplet flow to airflow, by weight, with a

uniform distribution at the inlet plane, of at least four percent.

Acceptable engine operation precludes flameout, run down, continued or

non-recoverable surge or stall, or loss of acceleration and

deceleration capability. It must also be shown after the ingestion that

there is no unacceptable mechanical damage, unacceptable power loss, or

other adverse engine anomalies. The rain ingestion must occur under the

following static ground level conditions:

(1) A normal stabilization period at take-off power without rain

ingestion, followed immediately by the suddenly commencing ingestion of

rain for three minutes at takeoff power, then

(2) Continuation of the rain ingestion during subsequent rapid

deceleration to minimum idle, then

(3) Continuation of the rain ingestion during three minutes at

minimum idle power to be certified for flight operation, then

(4) Continuation of the rain ingestion during subsequent rapid

deceleration to takeoff power.

(c) Engines for supersonic airplanes. In addition to complying with

paragraph (a)(1) of this section, a separate test for supersonic

airplane engines only, shall be conducted with three hailstones

ingested at supersonic cruise velocity. These hailstones shall be aimed

at the engine's critical face area, and their ingestion must not cause

unacceptable mechanical damage or unacceptable power or thrust loss

after the ingestion or require the engine to be shut down. The size of

these hailstones shall be determined from the linear variation in

diameter from 1-inch (25 millimeters) at 35,000 feet (10,500 meters) to

1/4-inch (6 millimeters) at 60,000 feet (18,000 meters) using the

diameter corresponding to the lowest expected supersonic cruise

altitude. Alternatively, three larger hailstones may be ingested at

subsonic velocities such that the kinetic energy of these larger

hailstones is equivalent to the applicable supersonic ingestion

conditions.

(d) For an engine that incorporates or requires the use of a

protection device, demonstration of the rain and hail ingestion

capabilities of the engine, as required in paragraphs (a), (b), and (c)

of this section, may be waived wholly or in part by the Administrator

if the applicant shows that:

(1) The subject rain or hail constituents are of a size that will

not pass through the protection device;

(2) The protection device will withstand the impact of the subject

water constituents; and

(3) The subject water constituents, stopped by the protective

device, will not obstruct the flow of induction air

[[Page 41694]]

into the engine, resulting in damage, power or thrust loss, or other

adverse engine anomalies in excess of what would be accepted in

paragraphs (a), (b), and (c) of this section.

9. Appendix B is added to part 33, to read as follows:

Appendix B to Part 33--Certification Standard Atmospheric

Concentrations of Rain and Hail

Figure B1, Table B1, Table B2, Table B3, and Table B4 specify

the atmospheric concentrations and size distributions of rain and

hail for establishing certification, in accordance with the

requirements of Sec. 33.78(a)(2). In conducting tests, normally by

spraying liquid water to simulate rain conditions and by delivering

hailstones fabricated from ice to simulate hail conditions, the use

of water droplets and hailstones having shapes, sizes and

distributions of sizes other than those defined in this Appendix B,

or the use of a single size or shape for each water droplet or

hailstone, can be accepted, provided the applicant shows that the

substitution does not reduce the severity of the test.

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[[Page 41695]]

Table B1.--Certification Standard Atmospheric Rain Concentrations

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

Rain water

content

(RWC)

Altitude (feet) (gramswater/

meter\3\

air)

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

0......................................................... 20.0

20,000.................................................... 20.0

26,300.................................................... 15.2

32,700.................................................... 10.8

39,300.................................................... 7.7

46,000.................................................... 5.2

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

RWC values at other altitudes may be determined by linear interpolation.

Note: Source of data--Results of the Aerospace Industries Association

(AIA) Propulsion Committee Study, Project PC 338-1, June 1990.

Table B2.--Certification Standard Atmospheric Hail Concentrations

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

Hail water

content

(HWC)

Altitude (feet) (grams

water /

meter\3\

air)

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

0.......................................................... 6.0

7,300...................................................... 8.9

8,500...................................................... 9.4

10,000..................................................... 9.9

12,000..................................................... 10.0

15,000..................................................... 10.0

16,000..................................................... 8.9

17,700..................................................... 7.8

19,300..................................................... 6.6

21,500..................................................... 5.6

24,300..................................................... 4.4

29,000..................................................... 3.3

46,000..................................................... 0.2

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

HWC values at other altitudes may be determined by linear

interpolation. The hail threat below 7,300 feet and above 29,000 feet

is based on linearly extrapolated data.

Note: Source of data--Results of the Aerospace Industries Association

(AIA) Propulsion Committee (PC) Study, Project (PC 338-1, June 1990.

Table B3.--Certification Standard Atmospheric Rain Droplet Size

Distribution

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

Contribution

Rain droplet diameter (mm) to total LWC

(%)

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

0-0.49.................................................... 0

0.50-0.99................................................. 2.25

1.00-1.49................................................. 8.75

1.50-1.99................................................. 16.25

2.00-2.49................................................. 19.00

2.50-2.99................................................. 17.75

3.00-3.49................................................. 13.50

3.50-3.99................................................. 9.50

4.00-4.49................................................. 6.00

4.50-4.99................................................. 3.00

5.00-5.49................................................. 2.00

5.50-5.99................................................. 1.25

6.00-6.49................................................. 0.50

6.50-7.00................................................. 0.25

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

Total................................................. 100.00

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

Median diameter of rain droplets is 2.66 mm

Note: Source of data--Results of the Aerospace Industry Association

(AIA) Propulsion Committee (PC) Study, Project PC 338-1, June 1990.

Table B4.--Certification Standard Atmospheric Hailstone Size

Distribution

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

Contribution

Hailstone diameter (mm) to total HWC

(%)

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

0.4.9..................................................... 0

5.0-9.9................................................... 17.00

10.0-14.9................................................. 25.00

15.0-19.9................................................. 22.50

20.0-24.9................................................. 16.00

25.0-29.9................................................. 9.75

30.0-34.9................................................. 4.75

35.0-39.9................................................. 2.50

40.0-44.9................................................. 1.50

45.0-49.9................................................. 0.75

50.0-55.0................................................. 0.25

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

Total................................................. 100.00

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

Median diameter of hailstones is 16 mm.

Note: Source of data--Results of the Aerospace Association (AIA)

Propulsion Committee (PC) Study, Project PC 338-1, June 1990.

Issued in Washington, DC on August 2, 1996.

Elizabeth Yoest,

Acting Director, Aircraft Certification Services.

[FR Doc. 96-20265 Filed 8-8-96; 8:45 am]

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