[Federal Register Volume 61, Number 155 (Friday, August 9, 1996)]
[Proposed Rules]
[Pages 41688-41695]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-20265]



[[Page 41687]]


_______________________________________________________________________

Part II





Department of Transportation





_______________________________________________________________________



Federal Aviation Administration



_______________________________________________________________________



14 CFR Parts 23, 25, and 33



Airworthiness Standards: Rain and Hail Ingestion Standards; Proposed 
Rule

  Federal Register / Vol. 61, No. 155 / Friday, August 9, 1996 / 
Proposed Rules  

[[Page 41688]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Parts 23, 25, and 33

[Docket No. 28652; Notice No. 96-12]
RIN 2120-AF75


Airworthiness Standards; Rain and Hail Ingestion Standards

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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

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

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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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[GRAPHIC] [TIFF OMITTED] TP09AU96.000


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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]
BILLING CODE 4910-13-M