Federal Register, Volume 61 Issue 155 (Friday, August 9, 1996)

[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

[[Page 41691]]

could achieve the desired result, and because engine design takes place
in the context of constant technological change. Based on discussions
with industry representatives, the FAA expects that, once rain/hail
centrifuging and engine cycle models are established, compliance would
be accomplished through design modifications that would have little
impact on manufacturing costs. Such design features may affect: (1) fan
blade/propeller, (2) spinner/nose cone, (3) bypass splitter, (4) engine
bleeds, (5) accessory loads, (6) variable stator scheduling, and (7)
fuel control. Similarly, the FAA expects that the rule would have a
negligible effect on operating costs (again, based on discussions with
industry representatives).

Expected Benefits

Rain or hail related in-flight engine shutdowns are rare
occurrences. This is due, in large part, to the high quality of
meteorological data available to ground controllers and pilots, and to
well established weather avoidance procedures. However, while such
events are infrequent, they pose a serious hazard because they
typically occur during a critical phase of flight where recovery is
difficult or impossible.
An examination of FAA and National Transportation Safety Board
(NTSB) records revealed two accidents that were the result of inflight
engine shutdowns or rundowns caused by excessive water ingestion. In
each case, the aircraft was in the descent phase of flight. These
accidents form the basis of the expected benefits of the proposed rule,
as summarized below. However, the following summary should be
considered a conservative estimate of the rule's potential benefits for
three reasons.
First, the rule should have the effect of increasing turbine engine
water ingestion tolerance regardless of the source of water. The
historical record shows that many accidents (not included in the
following benefit estimates) were caused by other forms of water such
as snow and graupel. It is possible that the aircraft in some of these
cases would have benefited from the proposed rule.
Second, several other incidents, while not resulting in a crash,
nevertheless had catastrophic potential. This potential could be
exacerbated by the development of more efficient turbofan powerplants
which have permitted large aircraft designs incorporating fewer
engines. An industry study identified seven events (not recorded in
either the FAA or NTSB databases) in which rain and/or hail affected
two or more engines and resulted in an inflight shutdown of at least
one engine.
Third, heavy rain and hail are often accompanied by severe
turbulence and windshear. While recovery from a water induced engine
shutdown is frequently successful, the ability to maintain engine power
during an encounter with an unexpected downdraft could be crucial to
avoiding a crash.

Benefits of Prevented Aircraft Damage

The available accident and aircraft usage data suggest the
categories that are used to classify the benefits of the proposed rule.
These classifications are: (1) Large air carrier aircraft (major and
national air carriers), and (2) other air carrier aircraft (large
regional, medium regional, commuter, and other small certificated air
carriers).
An examination of accident records for the period 1975-90,
indicates that, in the absence of the proposed rule, the probability of
a hull loss due to a water induced loss of engine power is 0.0104 per
million airplane departures for large air carriers, and 0.0276 per
million airplane departures for other air carriers.
The calculation of the rule's benefits, then, depends on the degree
to which the rule can reduce this risk. According to industry
representatives, compliance with the proposed standards would reduce
the accident rate by two orders of magnitude. That is, the rule is
expected to be 99 percent effective in reducing water ingestion
accidents. FAA estimates that the annual average benefits per airplane
from prevented aircraft damage would be approximately $337 and $97 for
large air carriers and other air carriers, respectively.

Benefits of Prevent Injuries and Fatalities

Using projections from the FAA Aviation Forecast, this analysis
assumes that the average large air carrier airplane has 168 seats and a
load factor of 61 percent. The average regional airplane is assumed to
have 30 seats and a load factor of 51 percent. The estimated
distribution of fatal, serious, and minor injuries is derived from the
actual distribution of casualties in the accidents cited above. On the
basis of these assumptions, FAA estimates the annual benefits of
prevented casualties per airplane would be $3,062 for operations by
large air carriers and $706 for operations by other air carriers.

Benefit-Cost Analysis

The benefits and costs of the proposed rule are compared for two
representative engine certifications using the following assumptions:
(1) For each certification, 50 engines are produced per year for 10
years (500 engines), (2) incremental certification costs are incurred
in year ``0'', (3) engine production begins in year ``3'', (4) the
first engines enter service in year ``4'', (5) each engine is retired
after 10 years, (6) the discount rate is 7 percent. Also, in order to
compare incremental engine costs with expected benefits (which are
expressed in terms of the reduction in the airplane accident rate) this
analysis assumes that each airplane has two engines.
For each airplane/engine type, the annual benefit per aircraft is
the sum of the expected property and casualty benefits. The total
benefit for each type certification, then, is the product of the per
aircraft annual benefit and the number of aircraft in service summed
over the life of the engines. Thus, for representative type
certifications, discounted lifecycle benefits would be approximately
$3.7 million and $0.8 million for operations by large air carriers and
other air carriers, respectively.
FAA finds that the rule would be cost-beneficial. Under
conservative production, service life, and incremental engine
certification cost assumptions, the expected discounted benefits of
prevented casualties and aircraft damage would exceed discounted costs
by a factor ranging from 5.5 ($3,661,084/$667,000) for operations by
large air carriers to 1.3 ($864,696/$667,000) for operations by other
air carriers.

Harmonization Benefits

In addition to the benefits of increased safety, the rule
harmonizes with JAR requirements, thus reducing costs associated with
certificating aircraft turbine engines to differing airworthiness
standards.

Regulatory Flexibility Determination

The Regulatory Flexibility Act (RFA) of 1980 was enacted by
Congress to ensure that small entities are not unnecessarily or
disproportionately burdened by Government regulations. The RFA requires
a Regulatory Flexibility Analysis if a rule is expected to have a
``significant economic impact on a substantial number of small
entities.'' Based on the standards and thresholds specified in
implementing FAA Order 2100.14A, Regulatory Flexibility Criteria and
Guidance, the FAA has determined that the rule would not have a
significant impact on a substantial number of small manufacturers or
operators because no turbine engine manufacturer is a ``small entity''
as defined in the order.

[[Page 41692]]

International Trade Impact Assessment

The rule would have little or no effect on trade for either U.S.
firms marketing turbine engines in foreign markets or foreign firms
marketing turbine engines in the U.S.

Federalism Implications

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

Conclusion

For the reasons discussed above, including the findings in the
Regulatory Flexibility Determination and the International Trade Impact
Analysis, the FAA has determined that this proposed regulation is not
significant under Executive Order 12866. In addition, the FAA certifies
that this proposal, if adopted, would not have a significant economic
impact, positive or negative, on a substantial number of small entities
under the criteria of the Regulatory Flexibility Act. This proposal is
not considered significant under DOT Regulatory Policies and Procedures
(44 FR 11034, February 26, 1979). An initial regulatory evaluation of
the proposal, including a Regulatory Flexibility Determination and
Trade Impact Analysis, has been placed in the docket. A copy may be
obtained by contacting the person identified under FOR FURTHER
INFORMATION CONTACT.

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

Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

In consideration of the foregoing, the Federal Aviation
Administration proposes to amend parts 23, 25, and 33 of the Federal
Aviation Regulations (14 CFR part 23, 14 CFR part 25, and 14 CFR part
33) as follows:

PART 23--AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND
COMMUTER CATEGORY AIRPLANES

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

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

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

Sec. 23.901 Installation.

* * * * *
(d) * * *
(2) Ensure that the capability of the installed engine to withstand
the ingestion of rain, hail, ice, and birds into the engine inlet is
not less than the capability established for the engine itself under
Sec. 23.903(a)(2).
* * * * *
3. Section 23.903 is amended by revising paragraph (a)(2) to read
as follows:

Sec. 23.903 Engines.

(a) * * *
(2) Each turbine engine must either--
(i) Comply with Sec. 33.77 and Sec. 33.78 of this chapter for an
airplane for which application for type certification is made on or
after [Insert effective date of final rule]; or
(ii) Comply with Sec. 33.77 of this chapter in effect on October
31, 1974, and must have a foreign object ingestion service history that
has not resulted in any unsafe condition for an airplane for which
application for type certification was made before [Insert effective
date of final rule]; or
(iii) Be shown to have a foreign object ingestion service history
in similar installation locations which has not resulted in any unsafe
condition.

Note: Sec. 33.77 of this chapter in effect on October 31, 1974,
was published in 14 CFR parts 1 to 59, Revised as of January 1,
1975. See 39 FR 35467; October 1, 1974.
* * * * *

PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES

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

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

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

Sec. 25.903 Engines.

Note: Sec. 33.77 of this chapter in effect on October 31, 1974,
was published in 14 CFR parts 1 to 59, Revised as of January 1,
1975. See 39 FR 35467; October 1, 1974.
* * * * *

PART 33--AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES

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

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

7. Section 33.77 is amended by revising paragraphs (c) and (e) to
read as follows:

Sec. 33.77 Foreign object ingestion.

* * * * *
(c) Ingestion of ice under the conditions prescribed in paragraph
(e) of this section, may not cause a sustained power or thrust loss or
require the engine to be shut down.
* * * * *
(e) Compliance with paragraphs (a), (b), and (c) of this section
must be shown by engine test under the following ingestion conditions:

----------------------------------------------------------------------------------------------------------------
Speed of foreign
Foreign object Test quantity object Engine operation Ingestion
----------------------------------------------------------------------------------------------------------------
Birds:
3-ounce size................ One for each 50 Liftoff speed of Takeoff........... In rapid sequence
square inches of typical aircraft. to simulate a
inlet area, or flock encounter
fraction thereof, and aimed at
up to a maximum selected critical
of 16 birds. areas.
Three-ounce bird
ingestion not
required if a 1\1/
2\-pound bird
will pass the
inlet guide vanes
into the rotor
blades.

[[Page 41693]]

1\1/2\-pound size........... One for the first Initial climb Takeoff........... In rapid sequence
300 square inches speed of typical to simulate a
of inlet area, if aircraft. flock encounter
it can enter the and aimed at
inlet, plus one selected critical
for each areas.
additional 600
square inches of
inlet area, or
fraction, thereof
up to a maximum
of 8 birds.
4-pound size................ One, if it can Maximum climb Maximum cruise.... Aimed at critical
enter the inlet. speed of typical area.
aircraft, if the
engine has inlet
guide vanes.
Liftoff speed of Takeoff........... Aimed at critical
typical aircraft, area.
if the engine
does not have
inlet guide
vanes.
Ice............................. Maximum Sucked in......... Maximum cruise.... To simulate a
accumulation on a continuous
typical inlet maximum icing
cowl and engine encounter at 25
face resulting deg.F.
from a 2-minute
delay in
actuating anti-
icing system, or
a slab of ice
which is
comparable in
weight or
thickness for
that size engine.
----------------------------------------------------------------------------------------------------------------
Note: The term ``inlet area'' as used in this section means the engine inlet projected area at the front face of
the engine. It includes the projected area of any spinner or bullet nose that is provided.

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

Sec. 33.78 Rain and hail ingestion.

(a) All engines. (1) The ingestion of large hailstones (0.8 to 0.9
specific gravity) at the maximum rough air speed, up to 15,000 feet
(4,500 meters), associated with a representative aircraft, with the
engine at maximum continuous power, may not cause unacceptable
mechanical damage or unacceptable power or thrust loss after the
ingestion, or require the engine to be shut down. One-half the number
of hailstones shall be aimed randomly over the inlet face area and the
other half aimed at the critical inlet fact area. The hailstone number
and size shall be determined as follows:
(i) One 1-inch (25 millimeters) diameter hailstone for engines with
inlet area of not more than 100 square inches (0.0645 square meters).
(ii) One 1-inch (25 millimeters) diameter and one 20-inch (50
millimeters) diameter hailstone for each 150 square inches (0.0968
square meters) of inlet area, or fraction thereof, for engines with
inlet area more than 100 square inches (0.0645 square meters).
(2) Except as provided in paragraph (b) of this section, it must be
shown that each engine is capable of acceptable operation throughout
its specified operating envelope when subjected to sudden encounters
with the certification standard concentrations of rain and hail, as
defined in Appendix B to this part. Acceptable engine operation
precludes flameout, run down, continued or non-recoverable surge or
stall, or loss of acceleration and deceleration capability during any
three minute continuous period in rain and during any 30 second
continuous period in hail. It must also be shown after the ingestion
that there is no unacceptable mechanical damage, unacceptable power or
thrust loss, or other adverse engine anomalies.
(b) Engines for rotocraft. As an alternative to the requirements
specified in paragraph (a)(2) of this section, for rotocraft turbine
engines only, it must be shown that each engine is capable of
acceptable operation during and after the ingestion of rain with an
overall ratio of water droplet flow to airflow, by weight, with a
uniform distribution at the inlet plane, of at least four percent.
Acceptable engine operation precludes flameout, run down, continued or
non-recoverable surge or stall, or loss of acceleration and
deceleration capability. It must also be shown after the ingestion that
there is no unacceptable mechanical damage, unacceptable power loss, or
other adverse engine anomalies. The rain ingestion must occur under the
following static ground level conditions:
(1) A normal stabilization period at take-off power without rain
ingestion, followed immediately by the suddenly commencing ingestion of
rain for three minutes at takeoff power, then
(2) Continuation of the rain ingestion during subsequent rapid
deceleration to minimum idle, then
(3) Continuation of the rain ingestion during three minutes at
minimum idle power to be certified for flight operation, then
(4) Continuation of the rain ingestion during subsequent rapid
deceleration to takeoff power.
(c) Engines for supersonic airplanes. In addition to complying with
paragraph (a)(1) of this section, a separate test for supersonic
airplane engines only, shall be conducted with three hailstones
ingested at supersonic cruise velocity. These hailstones shall be aimed
at the engine's critical face area, and their ingestion must not cause
unacceptable mechanical damage or unacceptable power or thrust loss
after the ingestion or require the engine to be shut down. The size of
these hailstones shall be determined from the linear variation in
diameter from 1-inch (25 millimeters) at 35,000 feet (10,500 meters) to
1/4-inch (6 millimeters) at 60,000 feet (18,000 meters) using the
diameter corresponding to the lowest expected supersonic cruise
altitude. Alternatively, three larger hailstones may be ingested at
subsonic velocities such that the kinetic energy of these larger
hailstones is equivalent to the applicable supersonic ingestion
conditions.
(d) For an engine that incorporates or requires the use of a
protection device, demonstration of the rain and hail ingestion
capabilities of the engine, as required in paragraphs (a), (b), and (c)
of this section, may be waived wholly or in part by the Administrator
if the applicant shows that:
(1) The subject rain or hail constituents are of a size that will
not pass through the protection device;
(2) The protection device will withstand the impact of the subject
water constituents; and
(3) The subject water constituents, stopped by the protective
device, will not obstruct the flow of induction air

[[Page 41694]]

into the engine, resulting in damage, power or thrust loss, or other
adverse engine anomalies in excess of what would be accepted in
paragraphs (a), (b), and (c) of this section.
9. Appendix B is added to part 33, to read as follows:

Appendix B to Part 33--Certification Standard Atmospheric
Concentrations of Rain and Hail

Figure B1, Table B1, Table B2, Table B3, and Table B4 specify
the atmospheric concentrations and size distributions of rain and
hail for establishing certification, in accordance with the
requirements of Sec. 33.78(a)(2). In conducting tests, normally by
spraying liquid water to simulate rain conditions and by delivering
hailstones fabricated from ice to simulate hail conditions, the use
of water droplets and hailstones having shapes, sizes and
distributions of sizes other than those defined in this Appendix B,
or the use of a single size or shape for each water droplet or
hailstone, can be accepted, provided the applicant shows that the
substitution does not reduce the severity of the test.

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[[Page 41695]]

Table B1.--Certification Standard Atmospheric Rain Concentrations
------------------------------------------------------------------------
Rain water
content
(RWC)
Altitude (feet) (gramswater/
meter\3\
air)
------------------------------------------------------------------------
0......................................................... 20.0
20,000.................................................... 20.0
26,300.................................................... 15.2
32,700.................................................... 10.8
39,300.................................................... 7.7
46,000.................................................... 5.2
------------------------------------------------------------------------
RWC values at other altitudes may be determined by linear interpolation.
Note: Source of data--Results of the Aerospace Industries Association
(AIA) Propulsion Committee Study, Project PC 338-1, June 1990.

Table B2.--Certification Standard Atmospheric Hail Concentrations
------------------------------------------------------------------------
Hail water
content
(HWC)
Altitude (feet) (grams
water /
meter\3\
air)
------------------------------------------------------------------------
0.......................................................... 6.0
7,300...................................................... 8.9
8,500...................................................... 9.4
10,000..................................................... 9.9
12,000..................................................... 10.0
15,000..................................................... 10.0
16,000..................................................... 8.9
17,700..................................................... 7.8
19,300..................................................... 6.6
21,500..................................................... 5.6
24,300..................................................... 4.4
29,000..................................................... 3.3
46,000..................................................... 0.2
------------------------------------------------------------------------
HWC values at other altitudes may be determined by linear
interpolation. The hail threat below 7,300 feet and above 29,000 feet
is based on linearly extrapolated data.
Note: Source of data--Results of the Aerospace Industries Association
(AIA) Propulsion Committee (PC) Study, Project (PC 338-1, June 1990.

Table B3.--Certification Standard Atmospheric Rain Droplet Size
Distribution
------------------------------------------------------------------------
Contribution
Rain droplet diameter (mm) to total LWC
(%)
------------------------------------------------------------------------
0-0.49.................................................... 0
0.50-0.99................................................. 2.25
1.00-1.49................................................. 8.75
1.50-1.99................................................. 16.25
2.00-2.49................................................. 19.00
2.50-2.99................................................. 17.75
3.00-3.49................................................. 13.50
3.50-3.99................................................. 9.50
4.00-4.49................................................. 6.00
4.50-4.99................................................. 3.00
5.00-5.49................................................. 2.00
5.50-5.99................................................. 1.25
6.00-6.49................................................. 0.50
6.50-7.00................................................. 0.25
-------------
Total................................................. 100.00
------------------------------------------------------------------------
Median diameter of rain droplets is 2.66 mm
Note: Source of data--Results of the Aerospace Industry Association
(AIA) Propulsion Committee (PC) Study, Project PC 338-1, June 1990.

Table B4.--Certification Standard Atmospheric Hailstone Size
Distribution
------------------------------------------------------------------------
Contribution
Hailstone diameter (mm) to total HWC
(%)
------------------------------------------------------------------------
0.4.9..................................................... 0
5.0-9.9................................................... 17.00
10.0-14.9................................................. 25.00
15.0-19.9................................................. 22.50
20.0-24.9................................................. 16.00
25.0-29.9................................................. 9.75
30.0-34.9................................................. 4.75
35.0-39.9................................................. 2.50
40.0-44.9................................................. 1.50
45.0-49.9................................................. 0.75
50.0-55.0................................................. 0.25
-------------
Total................................................. 100.00
------------------------------------------------------------------------
Median diameter of hailstones is 16 mm.
Note: Source of data--Results of the Aerospace Association (AIA)
Propulsion Committee (PC) Study, Project PC 338-1, June 1990.

Issued in Washington, DC on August 2, 1996.
Elizabeth Yoest,
Acting Director, Aircraft Certification Services.
[FR Doc. 96-20265 Filed 8-8-96; 8:45 am]
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