[Federal Register Volume 63, Number 58 (Thursday, March 26, 1998)]
[Rules and Regulations]
[Pages 14794-14801]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-7902]



[[Page 14793]]

_______________________________________________________________________

Part IV





Department of Transportation





_______________________________________________________________________



Federal Aviation Administration



_______________________________________________________________________



14 CFR Parts 23, 25 and 33



Airworthiness Standards; Rain and Hail Ingestion Standards; Final Rule

  Federal Register / Vol. 63, No. 58 / Thursday, March 26, 1998 / Rules 
and Regulations  

[[Page 14794]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Parts 23, 25 and 33

[Docket No. 28652; Amendment Nos. 23-53, 25-95, and 33-19]
RIN 2120-AF75


Airworthiness Standards; Rain and Hail Ingestion Standards

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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

SUMMARY: These amendments establish revisions to the Federal Aviation 
Administration's certification standards for rain and hail ingestion 
for aircraft turbine engines. These amendments address engine power-
loss and instability phenomena attributed to operation in extreme rain 
or hail that are not adequately addressed by current requirements. 
These amendments also generally harmonize these standards with rain and 
hail ingestion standards being amended by the Joint Aviation 
Authorities (JAA). These amendments establish nearly uniform standards 
for engines certified in the United States under 14 CFR part 33 and in 
the JAA countries under Joint Airworthiness Requirements-Engines (JAR-
E), thereby simplifying the certification of engine designs by the FAA 
and the JAA.

EFFECTIVE DATE: April 30, 1998.

FOR FURTHER INFORMATION CONTACT: John Fisher, 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 (781) 
238-7149; fax (781) 238-7199.

SUPPLEMENTARY INFORMATION:

Availability of Final Rules

    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 
(20002-512-1661), 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 web page at http://www.access.gpo.gov/
su__docs for access to recently published rulemaking documents.
    Any person may obtain a copy of this final rule 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 amendment 
number or document number of this final rule.
    Persons interested in being placed on the mailing list for future 
notices of proposed rulemaking and final rulemaking should request from 
the above office a copy of Advisory Circular No. 11-2A, Notices of 
Proposed Rulemaking Distribution System, that describes the application 
procedure.

Small Entity Inquiries

    The Small Business Regulatory Enforcement Fairness Act of 1996 
(SBREFA) requires the FAA to report inquiries from small entities 
concerning information on, and advice about, compliance with statutes 
and regulations within the FAA's jurisdiction, including interpretation 
and application of the law to specific sets of facts supplied by a 
small entity.
    If you are a small entity and have a question, contact your local 
FAA official. If you do not know how to contact your local FAA 
official, you may contact Charlene Brown, Program Analyst Staff, Office 
of Rulemaking, ARM-27, Federal Aviation Administration, 800 
Independence Avenue, SW, Washington, DC 20591, 1-888-551-1594. Internet 
users can find additional information on SBREFA in the ``Quick Jump'' 
section of the FAA's web page at http://www.faa.gov and may send 
electronic inquiries to the following internet address: 9-AWA-
[email protected].

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 when needed. All 
parties agreed to work in partnership to address jointly the 
harmonization task. This partnership was later expanded to include the 
airworthiness authority of Canada, Transport Canada.
    This partnership identified seven items which were 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

[[Page 14795]]

though one manufacturer expressed reservations. The FAA published a 
notice of proposed rulemaking on August 9, 1996 (61 FR 41688). This 
rule and associated advisory material reflect the ARAC recommendations.

Discussion of Comments

    All interested persons have been afforded an opportunity to 
participate in this rulemaking, and due consideration has been given to 
all comments received. The commenters represent domestic and foreign 
industry, and foreign airworthiness authorities. Five commenters 
provided the FAA with comments to the NPRM.
    Four commenters expressed concern with the proposed wording for 
Secs. 23.903 and 25.903. The commenters state that the proposal could 
result in retroactive requirements imposed on certain engines already 
type certificated. Three of the four commenters further state that this 
part of the proposal represents a significant departure from the 
proposal submitted to the FAA by ARAC.
    The FAA agrees. It was not the intent of the FAA to retroactively 
impose the new requirements on an engine design already type 
certificated unless service history indicates that an unsafe condition 
is present. The FAA has changed the wording for Secs. 23.903 and 25.903 
back to that originally proposed by the ARAC.
    All five commenters found a number of typographical errors and 
suggested some editorial changes. One notable typographical error 
appeared in the ``Disposition of Comments'' section of the preamble of 
the proposal. When addressing a concern that the hail threat definition 
was apparently rounded up to 10 g/m \3\, the value 8/3 g/m \3\ was 
incorrect and should have been written as 8.7 g/m \3\.
    The FAA also agrees to the other recommendations by the commenters 
and the following grammatical corrections and changes to Sec. 33.78 and 
Appendix B have been made to this rule:
    Section 33.78(a)(1): ``Critical inlet fact area'' has been changed 
to ``Critical inlet face area'' and the last sentence revised to read, 
``the hailstones shall be ingested in a rapid sequence to simulate a 
hailstone encounter and the number and size of the hailstones shall be 
determined as follows:''.
    Section 33.78(a)(1)(ii): The term ``one 20-inch'' has been changed 
to ``one 2-inch''.
    Section 33.78(a)(2): The following has been added to the beginning 
of the paragraph, ``In addition to complying with paragraph (a)(1) of 
this section and'', and a comma has been added immediately following 
the phrase ``or loss of acceleration and deceleration capability''.
    Section 33.78(b)(4): ``deceleration'' has been replaced with 
``acceleration''.
    Appendix B, Table B3: ``Contribution to total LWC (%)'' has been 
changed to ``Contribution to total RWC (%)''.
    Appendix B, Table B4: The term ``0.49'' has been changed to ``0-
4.9'', and ``hailstone'' has been replaced with ``hail'' in the title, 
column heading, and footnote.
    One commenter provided an additional clarifying statement with 
respect to the hail threat level variations obtained from the Industry 
Study. Given an extremely remote encounter probability and a typical 
thirty second exposure to severe hail, the assessed hail threat level 
varies from 8.7 g/m \3\ to 10.2 g/m \3\, depending upon the airspeed of 
the aircraft traversing the hail shaft.
    The FAA agrees with the commenter's additional explanation of the 
assessed hail threat variation. However, the discussion of the Industry 
Study in the proposal is technically correct.
    One commenter states the need for advisory material to accompany 
the rule to clarify various terms and criteria contained in the rule.
    The FAA agrees. An extensive advisory circular (AC) was drafted 
providing explanation of the various terms and criteria contained in 
the rule. The FAA issued a notice of availability of proposed AC and 
request for comments on September 5, 1996 (61 FR 46893). Further 
information regarding this AC can be obtained by contacting the FAA at 
the address specified under FOR FURTHER INFORMATION CONTACT:
    One commenter suggested changes to the preamble discussion 
regarding power loss and performance degradation. The commenter did not 
suggest nor imply that any changes to the proposed rule were needed. 
The FAA need not address those comments since they do not affect the 
meaning of these regulations.
    One commenter states that the criterion of no flameout contained in 
Sec. 33.78(a)(2) and Sec. 33.78(b) was excessive. The commenter further 
states that many engines are equipped with automatic re-ignition 
systems that would ensure quick recovery from a flameout.
    The FAA disagrees. Automatic re-ignition systems can facilitate 
quick recovery from a flameout as a result of a momentary ingestion, 
such as an ice shed. However, the rain and hail ingestion threats 
addressed by the new standards are not momentary, and have been defined 
for purposes of certification testing as 30 seconds duration for hail 
and 3 minutes duration for rain. Once flameout occurs under these 
conditions, it is unlikely that the engine will be capable of recovery 
until the ingestion of rain or hail ceases, with or without an 
automatic re-ignition system. Also, for actual encounters of severe 
rain and hail, it is likely that the engine will continue to ingest 
water, at lower concentrations, after exiting the area of severe rain 
or hail. The effect of this ingested water is to lower the starting 
capability of the engine. Therefore, if an airplane encounters severe 
rain or hail with installed engines that are susceptible to flameout, 
the airplane will be susceptible to an all engine out, forced landing. 
For these reasons, demonstrating tolerance to flameout under conditions 
of extreme rain and hail is a primary objective of the new standards.
    One commenter states that the acceptance criteria for rain and hail 
ingestion contained in Sec. 33.78(a)(2) and Sec. 33.78(b) appeared to 
be more stringent than the acceptance for ice ingestion. The commenter 
believes that the acceptance criteria for rain and hail ingestion 
should be less stringent than for ice ingestion, since ice ingestion is 
a more common occurrence than hail ingestion.
    The FAA concurs with the commenter that the stringency of 
acceptance criteria should be proportional to the occurrence rate of 
the threat being assessed. However, the FAA disagrees with the 
commenter's view that the acceptance criteria for rain and hail 
ingestion are more stringent than for ice ingestion. Some amount of 
sustained power or thrust loss is permitted following an ice ingestion 
test. Also, the FAA would accept momentary but recoverable surges and 
stalls encountered while testing to the new rain and hail ingestion 
standards, but has not historically accepted momentary surges and 
stalls following an ice ingestion test. Flameout, run down, continued 
or non-recoverable surge or stall, and loss of acceleration and 
deceleration are unacceptable conditions for rain, hail and ice 
ingestion.
    Finally, the FAA has made the following minor editorial changes to 
better align this rule with recent changes to the JAA's requirements. 
These changes do not affect the scope of the rule or change the intent 
of these sections.
    Section 33.78(a)(1): The phrase ``maximum true air speed'' replaces 
the phrase ``maximum rough air speed'', and the phrase ``operating in 
rough air'' is added following the words ``representative aircraft''.

[[Page 14796]]

    Section 33.78(a)(1)(i) and (ii): The word ``area'' is changed to 
read ``areas''.
    Section 33.78(c): In the first sentence the phrase ``complying with 
paragraph (a)(1) of this section'' is changed to read ``complying with 
paragraphs (a)(1) and (a)(2) of this section.
    Appendix B: The word ``hailstones'' is changed to read ``hail'' in 
the introductory paragraph and also in Table B4.
    After careful review of all the comments, the FAA has determined 
that air safety and the public interest require the adoption of the 
rule with the changes described.

Paperwork Reduction Act

    In accordance with the Paperwork Reduction Act of 1995 (44 U.S.C. 
3507(d), there are no information collection requirements associated 
with this final rule.

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) Will 
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) 
will not have a significant impact on a substantial number of small 
entities; and (4) will not constitute a barrier to international trade. 
These analyses, available in the docket, are summarized below.

Incremental Costs

    The proposed rule will permit a range of compliance options, 
thereby enabling manufacturers to select cost-minimizing approaches. 
Approaches that maximize the use of analytical methods will 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 will likely be the most costly. Incremental 
certification cost estimates supplied by industry varied depending on 
engine model and the testing method used.
    FAA conservatively estimates that incremental certification costs 
for an airplane turbine engine design will be approximately $627,000--
this includes $300,000 in additional engineering hours, and $327,000 
for the prorated share of the cost of a test facility.
    Based on statements from industry, the FAA expects that, once Rain/
Hail centrifuging and engine cycle models are established, compliance 
will be accomplished through design modifications that will 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 will have a 
negligible effect on operating costs.

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 the FAA accident/incident database system and 
National Transportation Safety Board (NTSB) records revealed two 
accidents that were the result of inflight engine shutdown 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 subject rule. However, what follows 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 Accident/
incident records show that many events (not included in the benefits 
estimates that follow) were caused by other forms of water such as snow 
and graupel. It is possible that some of these cases would have 
benefited from the subject 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.
    The available accident and aircraft usage data suggest the 
categories that are used to classify the benefits of the subject rule. 
These classifications are: (1) Large air carrier aircraft (operated by 
major and national air carriers), and (2) other air carrier aircraft 
(operated by large regional, medium regional, commuter, and other small 
certificated air carriers). An examination of accident records for the 
20-year period 1975-1994 indicates that, in the absence of the subject 
rule, the probability of a hull loss due to a water induced loss of 
engine power is 0.0094 per million departures for large air carriers, 
and 0.0249 per million 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 revised water ingestion standards 
will reduce the rate of engine power loss events by two orders of 
magnitude. This analysis assumes that the rule's effect on the accident 
rate will be proportionately equal to the rule's effect on the event 
rate.
    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%. The average regional air carrier airplane is 
assumed to have 30 seats and a load factor of 51%. The estimated 
distribution of fatal, serious, and minor injuries is based on 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 will be $3,360 for large air carriers 
and $618 for other air carriers.

Benefits and Costs Analysis

    The benefits and costs of the rule are compared for two 
representative engine certifications: (1) An engine designed for 
operation on a large jet transport (corresponding to the ``large air 
carrier'' category described earlier), and (2) an engine designed for 
operation on a regional transport (corresponding to the ``other air 
carrier'' category).
    For each certification, the following assumptions apply: (1) 50 
engines are produced per year for 10 years (500 total

[[Page 14797]]

engines produced per certification), (2) incremental certification 
costs are incurred in the year 2000, (3) engine production begins in 
the year 2002, (4) the first engines enter service in the year 2003, 
(5) each engine is retired after 10 years, (6) the discount rate is 7%. 
Also, in order to compare incremental engine costs with expected 
benefits (which are expressed in terms of the reduction in the aircraft 
accident rate) this analysis assumes that each aircraft has two 
engines.
    Under the assumptions enumerated above, total lifecycle benefits 
for a representative engine designed for operation on a large airplane 
equal approximately $9.3 million or $3.5 million at present value (1997 
dollars). Total lifecycle benefits for a representative engine designed 
for operation on a regional airplane equal to approximately $1.8 
million or $0.7 million at present value.
    This analysis postulates that incremental certification costs for 
both representative engine designs are the same. As discussed above, 
incremental costs are approximately $627,000 or $512,000 at present 
value.
    FAA finds that the rule would be cost-beneficial. Under very 
conservative production, service life, and incremental engine 
certification cost assumption, the expected discounted benefits of 
prevented casualties and aircraft damage will exceed costs by a ratio 
ranging from 6.9 to 1 for large air carriers to 1.3 to 1 for 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 of 1980 establishes ``as a principle 
of regulatory issuance that agencies shall endeavor, consistent with 
the objective of the rule and of applicable statutes, to fit regulatory 
and informational requirements to the scale of the businesses, 
organizations, and governmental jurisdictions subject to regulation.'' 
To achieve that principal, the Act requires agencies to solicit and 
consider flexible regulatory proposal and to explain the rational for 
their actions. The Act covers a wide range of small entities, including 
small businesses, non-for-profit organizations and small governmental 
jurisdictions.
    Agencies must perform an analysis to determine whether a rule will 
have a significant economic impact on a substantial number of small 
entities; if the determination is that it will, the agency must prepare 
a regulatory flexibility analysis (RFA).
    However, if after an analysis for a proposed or final rule, an 
agency determines that a rule is not expected to have a significant 
economic impact on a substantial number of small entities. Section 
605(b) of the 1980 act provides that the head of the agency may so 
certify. The certification must include a statement providing the 
factual basis for this determination, and the reasoning should be 
clear.
    The FAA conducted the required preliminary analysis of the proposal 
and determined that it would not have a significant economic impact on 
a substantial number of small entities. That determination was 
published in the Federal Register on August 9, 1996 as part of the 
Notice of Proposed Rulemaking. No comments were received regarding the 
economic analysis of the rule. No substantial changes were made in the 
final rule from the proposed rule, and estimated costs were not 
significantly modified. Accordingly, pursuant to the Regulatory 
Flexibility Act, 5 U.S.C. 605(b), the Federal Aviation Administration 
certifies that this rule will not have a significant economic impact on 
a substantial number of small entities.

International Trade Impact Assessment

    The rule will 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. Generally, this rule harmonizes 
FAA requirements with existing and proposed JAA requirements.

Federalism Implication

    The regulations will not have substantial direct effects on the 
states, on the relationship between the national government and the 
states, or on the distribution of power and responsibilities among the 
various levels of government. Therefore, in accordance with Executive 
Order 12612, it is determined that this rule will not have sufficient 
federalism implications to warrant the preparation of a Federalism 
Assessment.

Unfunded Mandates Reform Act

    Title II of the Unfunded Mandates Reform Act of 1995 (The Act), 
enacted as Public L. 104-4 on March 22, 1995, requires each federal 
agency, to the extent permitted by law, to prepare a written assessment 
of the effects of any federal mandate in a proposed or final agency 
rule that may result in the expenditure by state, local, and tribal 
governments, in the aggregate, or by the private sector, of $100 
million or more (adjusted annually for inflation) in any one year. 
Section 204(A) of The Act, 2 U.S.C. 1534(A), requires the federal 
agency to develop an effective process to permit timely input by 
elected officers (or their designees) of state, local, and tribal 
governments on a proposed ``significant intergovernmental mandate''. A 
``significant intergovernmental mandate'' under The Act is any 
provision in a federal agency regulation that will impose an 
enforceable duty upon state, local, and tribal governments, in the 
aggregate, of $100 million (adjusted annually for inflation) in any one 
year. Section 203 of The Act, 2 U.S.C. 1533, which supplements section 
204(A), provides that before establishing any regulatory requirements 
that might significantly or uniquely affect small governments, the 
agency shall have developed a plan that, among other things, provides 
for notice to potentially affected small governments, if any, and for a 
meaningful and timely opportunity to provide input in the development 
of regulatory proposals.
    The FAA determines that this rule does not contain a significant 
intergovernmental or private sector mandate as defined by the act.

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

    Air transportation, Aircraft, Aviation safety, Safety.

Adoption of the Amendments

    In consideration of the foregoing, the Federal Aviation 
Administration amends 14 CFR parts 23, 25, and 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

[[Page 14798]]

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 Secs. 33.77 and 33.78 of this chapter in effect on 
April 30, 1998; or as subsequently amended; or
    (ii) Comply with Sec. 33.77 of this chapter in effect on October 
31, 1974, or as subsequently amended prior to April 30, 1998, and must 
have a foreign object ingestion service history that has not resulted 
in any unsafe condition; 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 Secs. 33.77 and 33.78 of this chapter in effect on 
April 30, 1998 or as subsequently amended; or
    (ii) Comply with Sec. 33.77 of this chapter in effect on October 
31, 1974, or as subsequently amended prior to April 30, 1998, and must 
have a foreign object ingestion service history that has not resulted 
in any unsafe condition; 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                                               
        Foregin object           Test quantity        object             Engine operation           Ingestion   
----------------------------------------------------------------------------------------------------------------
Birds:                                                                                                          
    3-ounce size.............  One for each 50   Liftoff speed of  Takeoff....................  In rapid        
                                square inches     typical                                        sequence to    
                                of inlet area,    aircraft.                                      simulate a     
                                or fraction                                                      flock encounter
                                thereof, up to                                                   and aimed at   
                                a maximum of 16                                                  selected       
                                birds. Three-                                                    critical areas.
                                ounce bird                                                                      
                                ingestion not                                                                   
                                required if a                                                                   
                                1\1/2\-pound                                                                    
                                bird will pass                                                                  
                                the inlet guide                                                                 
                                vanes into the                                                                  
                                rotor blades.                                                                   
    1\1/2\-pound size........  One for the       Initial climb     Takeoff....................  In rapid        
                                first 300         speed of                                       sequence to    
                                square inches     typical                                        simulate a     
                                of inlet area,    aircraft.                                      flock encounter
                                if it can enter                                                  at selected    
                                the inlet, plus                                                  critical areas.
                                one for each                                                                    
                                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        
                                enter the inlet.  speed of                                       critical area. 
                                                  typical                                                       
                                                  aircraft, if                                                  
                                                  the engine has                                                
                                                  inlet guide                                                   
                                                  vanes.                                                        
                                                 Liftoff speed of  Takeoff....................  Aimed at        
                                                  typical                                        critical area. 
                                                  aircraft, if                                                  
                                                  the engine does                                               
                                                  not have inlet                                                
                                                  guide vanes.                                                  
Ice:                                                                                                            
    Maximum accumulation on a  Sucked in.......  ................  Maximum cruise.............  To simulate a   
     typical inlet cowl and                                                                      continuous     
     engine face resulting                                                                       maximum icing  
     from a 2-minute delay in                                                                    encounter at 25
     actuating anti-icing                                                                        deg. F.        
     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.                 


[[Page 14799]]

    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 true air speed, up to 15,000 feet 
(4,500 meters), associated with a representative aircraft operating in 
rough air, 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 face area. The 
hailstones shall be ingested in a rapid sequence to simulate a 
hailstone encounter and the number and size of the hailstones shall be 
determined as follows:
    (i) One 1-inch (25 millimeters) diameter hailstone for engines with 
inlet areas of not more than 100 square inches (0.0645 square meters).
    (ii) One 1-inch (25 millimeters) diameter and one 2-inch (50 
millimeters) diameter hailstone for each 150 square inches (0.0968 
square meters) of inlet area, or fraction thereof, for engines with 
inlet areas of more than 100 square inches (0.0645 square meters).
    (2) In addition to complying with paragraph (a)(1) of this section 
and 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 rotorcraft. As an alternative to the requirements 
specified in paragraph (a)(2) of this section, for rotorcraft 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 
acceleration to takeoff power.
    (c) Engines for supersonic airplanes. In addition to complying with 
paragraphs (a)(1) and (a)(2) 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 and 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 
rain and hail constituents; and
    (3) The subject of rain and hail constituents, stopped by the 
protection device, will not obstruct the flow of induction air 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 
hail fabricated from ice to simulate hail conditions, the use of 
water droplets and hail 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 hail, can be 
accepted, provided that applicant shows that the substitution does 
not reduce the severity of the test.

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[[Page 14800]]

[GRAPHIC] [TIFF OMITTED] TR26MR98.000



BILLING CODE 4910-13-C


    Table B1.--Certification Standard Atmospheric Rain Concentrations   
------------------------------------------------------------------------
                                                                  Rain  
                                                                 water  
                                                                content 
                                                                 (RWC)  
                       Altitude (feet)                           (grams 
                                                                 water/ 
                                                               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)                    total RWC 
                                                                 (%)    
------------------------------------------------------------------------
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 in 2.66 mm                             
Note: Source of data--Results of the Aerospace Industries Association   
  (AIA Propulsion Committee (PC) Study, Project PC 338-1, June 1990.    


  Table B4.--Certification Standard Atmospheric Hail Size Distribution  
------------------------------------------------------------------------
                                                            Contribution
                    Hail diameter (mm)                        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 

[[Page 14801]]

                                                                        
45.0-49.9.................................................         0.75 
50.0-55.0.................................................         0.25 
                                                           -------------
    Total.................................................       100.00 
------------------------------------------------------------------------
Median diameter of hail is 16 mm                                        
Note: Source of data--Results of the Aerospace Industries Association   
  (AIA Propulsion Committee (PC) Study, Project PC 338-1, June 1990.    

    Issued in Washington, DC, on March 20, 1998.
Jane F. Garvey,
Administrator.
[FR Doc. 98-7902 Filed 3-25-98; 8:45 am]
BILLING CODE 4910-13-M