[Federal Register Volume 60, Number 43 (Monday, March 6, 1995)]
[Proposed Rules]
[Pages 12360-12363]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-5419]




[[Page 12359]]

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Part VIII





Department of Transportation





_______________________________________________________________________



Federal Aviation Administration



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14 CFR Part 33



Airworthiness Standards: Windmilling and Rotor Locking Tests, and 
Vibration and Vibration Tests; Proposed Rule

Federal Register / Vol. 60, No. 43 / Monday, March 6, 1995 / Proposed 
Rules  
[[Page 12360]] 

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 33

[Docket No. 28107; Notice No. 95-3]
RIN 2120-AF57


Airworthiness Standards; Windmilling and Rotor Locking Tests, and 
Vibration and Vibration Tests

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: The Federal Aviation Administration (FAA) proposes to change 
the windmilling and vibration airworthiness standards for the issuance 
of original and amended type certificates for aircraft engines. This 
proposal resulted from an effort to harmonize the Federal Aviation 
Regulations with European requirements being drafted by the Joint 
Aviation Authorities (JAA). The proposed changes, if adopted, would 
create one set of common requirements, that would reduce the regulatory 
burden on the aviation industry worldwide by eliminating the need for 
applicants for type certificates to comply with different sets of 
standards when seeking certifications from the FAA and JAA.

DATES: Comments must be submitted on or before June 5, 1995.

ADDRESSES: Comments on this notice should be mailed in triplicate to: 
Federal Aviation Administration, Office of the Chief Counsel, 
Attention: Rules Docket (AGC-200), Docket No. 28107, 800 Independence 
Avenue, SW., Washington, DC 20591. Comments delivered must be marked 
Docket No. 28107. Comments may be inspected in Room 915G weekdays 
between 9:00 a.m. and 5:00 p.m., except on Federal holidays.

FOR FURTHER INFORMATION CONTACT: John Golinski or 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 01803-5299; 
telephone (617) 238-7119; fax (617) 238-7199.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to submit written data, views, or 
arguments on this proposed rule. 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 
should identify the regulatory docket number and should be submitted in 
triplicate to the Rules Docket address specified above. all comments 
received on or before the closing date for comments specified will be 
considered by the Administrator before taking action on this proposed 
rulemaking. The proposals contained in this notice may be changed in 
light of comments received. All comments received will be available, 
both before and after the closing date for comments, in the Rules 
Docket for examination by interested persons. A report summarizing each 
substantive public contact with FAA personnel concerned with this 
rulemaking will be filed in the docket. Comments submitted in response 
to this notice must include a preaddressed, stamped postcard on which 
the following statement is made: ``Comments to Docket No. 28107.'' The 
postcard will be date stamped and mailed to the commenter.

Availability of NPRM's

    Any person may obtain a copy of this NPRM by submitting a request 
to the Federal Aviation Administration, Office of Public Affairs, 
Attention: Public Inquiry Center, APA-200, 800 Independence Avenue, 
SW., Washington, DC 20591, or by calling (202) 267-3484. Communications 
must identify the notice number of this NPRM.
    Persons 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, 
which describes the application procedure.

Background

    Part 33 of title 14 of the Code of Federal Regulations (14 CFR part 
33, hereafter ``part 33'') prescribes airworthiness standards for the 
issuance of original and amended type certificates for aircraft 
engines. Part E of the Joint Aviation Requirements (JAR-E) prescribes 
corresponding airworthiness standards of the European Joint Aviation 
Authorities (JAA). While part 33 and JAR-E are similar, they differ in 
several respects. Non-uniform standards impose a regulatory burden on 
applicants seeking certification under both sets of standards in the 
form of additional costs and delays in the time required for 
certification.
    As part of its commitment to promote harmonization of part 33 and 
JAR-E, the FAA, with the cooperation of the JAA, established the part 
33/JAR-E Authorities Engine Group to compare part 33 and JAR-E. This 
group included regulatory representatives from France, Canada, Germany, 
the United Kingdom, and the United States. The basis for the comparison 
was part 33, as amended through Amendment 11, and JAR-E, as amended 
through Change 7. As its initial effort, the study group focused on gas 
turbine engines and concentrated on JAR-E items that appeared to be 
more stringent than part 33. The identified differences were 
categorized into lists 1 and 2. List 1 included twenty items where the 
differences appear to be sufficiently significant to cause the JAA to 
apply additional conditions to U.S. manufacturers seeking JAA 
certification. List 2 included requirements considered to be equivalent 
to the corresponding Federal Aviation Regulation (FAR) in part 33 based 
on FAA policy and practice.
    In August 1989, at the request of the Aerospace Industries 
Association (AIA) and the Association Europeene Des Constructeurs De 
Materiel Aerospatial (AECMA), the FAA and JAA met in Paris, France, 
with aerospace industry representatives to initiate a process for 
resolving List 1 comparison issues. At an FAA/JAA management meeting in 
June 1992, in Toronto, Canada, seven part 33 engine ``Harmonization's 
Terms of Reference'' were introduced. Two of these initiatives, 
windmilling and rotor locking test requirements, and vibration and 
vibration test requirements, were contained in the FAA/JAA List 1 of 
twenty items. They were the first engine harmonization initiatives for 
which consensus was reached by study groups from domestic and 
international industry and airworthiness authorities. In December 1992, 
the FAA requested the Aviation Rulemaking Advisory Committee (ARAC) to 
further evaluate the proposals (57 FR 58840). This task, in turn, was 
assigned to the Propulsion Harmonization Working Group of ARAC. On June 
18, 1993, the working group reported to the ARAC, which recommended to 
the FAA that the FAA proceed with rulemaking. This NPRM and a 
corresponding notice of proposed amendment (NPA) to JAR-E reflect the 
ARAC recommendations.

General Discussion of the Proposals

    The proposals in the NPRM would harmonize U.S. regulations with 
existing and proposed requirements of the European Joint Aviation 
Authorities, codify current industry practices, and clarify existing 
requirements. Specifically, whey would (1) Clarify the existing 
requirement that excessive vibratory stresses may not be induced 
[[Page 12361]] throughout the declared flight envelope of the engine; 
(2) require that continued windmilling following engine shutdown must 
not create a hazard for the airplane; (3) expand the scope of vibration 
tests; (4) expand the applicability of rotor locking tests; and (5) 
clarify rotor locking and vibration test requirements.

Windmilling and Rotor Locking Test Requirements

Section 33.74  Windmilling
    Parts 23 and 25 of title 14 of the CFR prescribe the airworthiness 
standards for airplanes. Sections 23.903(e)(2) and 25.903(c) in part, 
state that for turbine engine installations, the means for stopping the 
rotation of any engine need be provided only where continued rotation 
could jeopardize the safety of the airplane. JAR-E presently provides a 
safety objective for windmilling without oil.
    This proposal would add a new section to state specific windmilling 
requirements that are consistent with the safety objectives of the 
airplane requirements in Secs. 23.903(e)(2) and 25.903(c), which 
address control of engine rotation. The proposed new requirements would 
ensure that windmilling following engine shutdown in flight would not 
create a hazard for the airplane.
    This proposal was developed and agreed to by the ARAC Propulsion 
Harmonization working group. The proposed change contains language that 
would be common to the language proposed for JAR-E, thereby 
establishing equivalency and creating consistency between the two 
regulations. In addition, because an engine manufacturer must show 
compliance to the proposed Sec. 33.74 which has safety objectives 
consistent with the corresponding airplane requirements for windmilling 
engines identified in Secs. 23.903(e)(2) and 25.903(c), the engine 
manufacturer can provide this information directly to the airplane 
manufacturers to reduce the amount of analysis performed by the 
airplane manufacturers under Secs. 23.903(e)(2) and 25.903(c), which 
could result in potential cost savings for the airplane manufacturers.
Section 33.92  Rotor Locking Tests
    Section 33.92 currently specifies engine test requirements for 
engines installed on supersonic aircraft and also specifies an 
endurance test for turbine engine rotor stopping and locking devices. 
This proposal would delete the test requirements in Sec. 33.92(a) and 
clarify the endurance test for rotor stopping and locking devices, that 
is applicable to all turbine engines that incorporate such a device. 
This proposed requirement will also be proposed in JAR-E, thereby 
harmonizing with part 33 and facilitating the harmonization of part 25 
with JAR 25, by allowing deletion of JAR 25.903(c)(1), which addresses 
continued windmilling after loss of engine oil.
    The proposed deletion of current Sec. 33.92(a) is based on the 
service experience of the world's only supersonic commercial transport. 
The British/French Concorde has experienced a number of inflight engine 
shutdowns at supersonic speeds since 1974. In each of these incidents, 
because of the aerodynamic effect of drag and loss of thrust, speed was 
rapidly reduced to subsonic levels. Therefore, requirements for 
conducting prolonged engine windmilling tests at supersonic speeds are 
unnecessary.
    The proposal would move the requirement that each engine 
incorporating a rotor locking device be shut down while operating at 
rated maximum continuous thrust from Sec. 33.92(b)(1) to proposed 
Sec. 33.92. Proposed revision Sec. 33.92 would also require that the 
means for stopping and locking the rotor(s) must be operated as 
specified in the engine operating instructions.
    The proposed revision to Sec. 33.92 would clarify the endurance 
test requirements currently identified in Sec. 33.92(b) by establishing 
that following rotor locking, the rotor(s) must be held stationary for 
five minutes while being subjected to the maximum torque that could 
result from continued flight in this condition. The harmonization 
review has established that the current requirement does not provide 
adequate information on how to run the test. Clarification is provided 
by the addition of a five minute test to confirm the durability of the 
system.

Vibration and Vibration Test Requirements

Section 33.63  Vibration
    Section 33.63 currently contains vibration design and construction 
standards for aircraft engines. This proposal would clarify the 
existing text by adding the term ``declared flight envelope'' to ensure 
that excessive vibration stresses are not induced at all intended 
airborne and non-airborne conditions of operation. This proposal would 
harmonize the vibration requirements.
Section 33.83  Vibration Test
    Section 33.83 prescribes the testing requirements that turbine 
engines must undergo to establish the aerodynamically induced system 
vibration (flutter) as well as the mechanically induced vibration 
characteristics of components that could induce failure. This proposal 
would delete the existing text and replace it with harmonized 
requirements. The harmonized requirements address some conditions that 
are currently being addressed by analysis in Sec. 33.75.
    Section 33.83(a). This proposal would replace the current text with 
new harmonized text to clarify the existing requirement that all 
components in each engine that may be subject to mechanically or 
aerodynamically induced vibratory excitations must undergo vibration 
surveys. These engine surveys shall be based upon an appropriate 
combination of experience, analysis, and component test and should 
address, as a minimum, blades, vanes, rotor discs, spacers, and rotor 
shafts. Substantive pre-certification activity (tests and analyses) is 
necessary for determining which engine components require verification 
by the engine certification process. The proposal retains the current 
practice of the FAA and JAA of limiting formal certification test 
requirements to only the final engine or major assembly rig vibration 
test.
    The proposal would replace the phrase ``at the maximum inlet 
distortion limit'' with ``throughout the declared flight envelope'' to 
clarify that the engine must be tested to cover all intended airborne 
and non-airborne conditions of operation. Using the term ``declared 
flight envelope'' better describes the airworthiness objective of this 
section. This change results in no foreseen additional burden on 
applicants because industry practice has been to conduct vibration 
surveys throughout the declared flight envelope. This proposal would 
also move the requirement specifying the range of rotor speeds and 
power or thrust of the vibration surveys from current Sec. 33.83(a) to 
proposed revised Sec. 33.83(b).
    Section 33.83(b). This proposal would revise this paragraph to 
reorganize and elaborate on existing requirements, introduce 
terminology relevant to flutter vibration, and achieve harmonization 
where differences currently exist between Part 33 and JAR-E. The 
proposed paragraph (b) would require the vibration tests to cover the 
ranges of physical rotor speeds, corrected rotor speeds, and engine 
power or thrust corresponding to operations throughout 
[[Page 12362]] the declared flight envelope from idling speed up to 103 
percent of the maximum rotor speed permitted for rating periods of 2 
minutes or longer, and up to 100 percent of all other rotor speeds. The 
proposal would also add to the revised paragraph (b) a requirement that 
if there is any indication of a stress peak arising at high physical or 
corrected rotational speeds, the surveys shall be extended. If it 
becomes physically impossible to achieve these extended rotor speeds, 
it would have to be shown by analysis or other means that no harmful 
vibration exists. Engine manufacturing and build tolerances can result 
in peak stresses occurring at slightly different rotor speeds between 
engines and engine parts (i.e., blades) of the same type design. The 
speed extension, therefore, is intended to cover inherent engine-to-
engine and blade-to-blade variations in vibratory response.
    Section 33.83(c). The proposal would revise the current paragraph 
(c) and reword the existing text to harmonize and clarify the existing 
requirement. Current paragraph (c) requires that during the vibration 
test, each accessory drive and mounting attachment must be loaded with 
the load imposed by each accessory used only for aircraft service up to 
the limit load specified by the applicant for the engine drive or 
attachment point. The proposal would require that evaluations be made 
of the effects on vibration characteristics of operating with scheduled 
changes (including tolerances) to variable vane angles, compressor 
bleeds, accessory loading, the most adverse inlet air flow distortion 
pattern declared by the manufacturer, and the most adverse conditions 
in the exhaust duct(s).
    Section 33.83(d) This proposal would add a new paragraph (d) that 
would require that the effects on vibration characteristics of likely 
fault conditions shall be evaluated by test, or analysis, or by 
reference to previous experience and be shown not to create a hazardous 
condition. Since U.S. engine manufacturers presently address and 
evaluate the effects of vibration characteristics through analysis in 
accordance with the requirements of Sec. 33.75, this proposal would 
harmonize part 33 with JAR-E.
    Section 33.83(e). This proposal would add a new paragraph (e). The 
current Sec. 33.83(b) requires that vibration stresses of rotor and 
stator components be less, by a margin acceptable to the Administrator, 
than the endurance limit of the material from which these parts are 
made, adjusted for the most severe operating conditions. This proposal 
would slightly modify the text of the requirement by incorporating the 
standard industry practice of making due allowance for variations in 
material properties. Current industry practice is based on the FAA 
interpretation of the current requirement. The vibration stresses 
associated with the vibration characteristics determined under 
Sec. 33.83 must be less than the endurance limits of the materials 
concerned, after making certain allowances. The suitability of these 
stress margins would have to be justified for each part and if it is 
determined that certain operating conditions, or ranges, need to be 
limited, operating and installation limitations would be established. 
The proposed new paragraph (e) would harmonize with existing JAR-E-650 
provisions and conform with current component vibration testing 
practices.
    Section 33.83(f). Proposed new paragraph (f) would require that 
compliance with Sec. 33.83 be substantiated for each specific 
installation configuration that can affect the vibration 
characteristics of the engine. The proposed language would provide that 
if these vibrations cannot be fully investigated during engine 
certification, then the methods by which they can be evaluated and 
compliance shown shall be substantiated and defined in the installation 
documents required by Sec. 33.5. The proposed amendment would codify 
current industry practice.

Paperwork Reduction Act

    In accordance with the Paperwork Reduction Act of 1990 (44 U.S.C. 
3501 et seq.), an evaluation of the paperwork burden of this proposal 
is not required since there are no recordkeeping or reporting 
requirements associated with this proposed rule.

Preliminary Regulatory Evaluation, Initial Regulatory Flexibility 
Determination, and Trade Impact Assessment

    Proposed changes to Federal regulations must undergo several 
economic analysis. First, Executive Order 12866 directs that each 
Federal agency 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 effect of regulatory changes on international trade. In conducting 
these analyses, the FAA has determined that this rule (1) Would 
generate benefits outweighing its costs; (2) is not a ``significant 
regulatory action'' as defined in the Executive Order; (3) is not 
``significant'' as defined in DOT's policies and procedures; (4) would 
not have a significant impact on a substantial number of small 
entities; and (5) would not constitute a barrier to international 
trade. These analyses, available in the docket, are summarized below.

Regulatory Evaluation Summary

    Of the several proposals, only one might result in additional cost. 
The FAA has identified the requirements in proposed Sec. 33.83(b) as 
the only one that could require minor additional engine testing and 
engineering analysis, resulting in negligible compliance costs. The 
reference to experience, analysis, and component tests in proposed 
Sec. 33.83(a) should not impose additional costs since it incorporates 
current industry practice. The revised engine windmilling requirements 
of proposed new Sec. 33.74 and the proposed amendments to Sec. 33.92(a) 
could potentially result in cost savings to engine and transport 
airplane manufacturers. The FAA solicits comments from interested 
persons on the costs of the proposed rule.
    The primary benefits of the proposed rule would be harmonization of 
airworthiness standards with the European Joint Aviation Requirements 
and clarification of existing standards. The resulting increased 
uniformity of standards would simplify airworthiness approval for 
import and export purposes and would avoid some of the costs that can 
result when manufacturers seek type certification under both sets of 
standards. While not readily quantifiable, the cost economies of 
harmonization would far exceed the minor incremental costs of the 
proposed rule.

Regulatory Flexibility Determinations

    The Regulatory Flexibility Act of 1980 (RFA) was enacted by 
Congress to ensure that small entities are not unnecessarily or 
disproportionately burdened by Federal regulations. The RFA requires a 
Regulatory Flexibility Analysis if a proposed rule would have a 
significant economic impact, either detrimental or beneficial, on a 
substantial number of small entities. Based on thresholds in 
implementing FAA Order 2100. 14A, Regulatory Flexibility Criteria and 
Guidance, the FAA has determined that the proposed rule would not have 
a significant economic impact on a substantial number of small 
entities. [[Page 12363]] 

International Trade Impact Assessment

    The proposed rule would not constitute a barrier to international 
trade, including the export of U.S. aircraft engines to foreign 
countries and the import of foreign aircraft engines into the United 
States. Instead, the proposed standards would harmonize with existing 
and proposed standards of foreign authorities, thereby lessening 
restraints on trade.

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 Evaluation and the International Trade Impact Assessment, 
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, will not have a significant economic impact, 
positive or negative, on a substantial number of small entities under 
the criteria of the Regulatory Flexibility Act. 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 
International Trade Impact Assessment, 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 Part 33

    Aircraft, Aviation safety.

The Proposed Amendment

    In consideration of the foregoing, the Federal Aviation 
Administration proposes to amend 14 CFR part 33 as follows:

PART 33--AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES

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

    Authority: 49 U.S.C. 1344, 1354(a), 1355, 1421, 1423, 1424, 
1425; 49 U.S.C. 106(g).

    2. Section 33.63 is revised to read as follows:


Sec. 33.63   Vibration.

    Each engine must be designed and constructed to function throughout 
its declared flight envelope and operating range of rotational speeds 
and power/thrust, without inducing excessive stress in any engine part 
because of vibration and without imparting excessive vibration forces 
to the aircraft structure.
    3. A new section 33.74 is added to read as follows:


Sec. 33.74   Windmilling.

    If the engine continues to windmill after it is shut down for any 
reason while in flight, continued windmilling of that engine must not 
result in damage that could create a hazard to aircraft representing a 
typical installation during the maximum period of flight likely to 
occur with that engine inoperative.
    4. Section 33.83 is revised to read as follows:


Sec. 33.83   Vibration test.

    (a) Each engine must undergo vibration surveys to establish that 
the vibration characteristics of those components that may be subject 
to mechanically or aerodynamically induced vibratory excitations are 
acceptable throughout the declared flight envelope. The engine surveys 
shall be based upon an appropriate combination of experience, analysis, 
and component test and shall address, as a minimum, blades, vanes, 
rotor discs, spacers, and rotor shafts.
    (b) The surveys shall cover the ranges of power or thrust, and both 
the physical and corrected rotational speeds for each rotor system, 
corresponding to operations throughout the range of ambient conditions 
in the declared flight envelope, from the minimum rotor speed up to 103 
percent of the maximum rotor speed permitted for rating periods of two 
minutes or longer, and up to 100 percent of all other permitted rotor 
speeds, including those that are overspeeds. If there is any indication 
of a stress peak arising at high physical or corrected rotational 
speeds, the surveys shall be extended in order to quantify the 
phenomenon and to ensure compliance with the requirements of 
Sec. 33.63.
    (c) Evaluations shall be made of the effects on vibration 
characteristics of operating with scheduled changes (including 
tolerances) to variable vane angles, compressor bleeds, accessory 
loading, the most adverse inlet air flow distortion pattern declared by 
the manufacturer, and the most adverse conditions in the exhaust 
duct(s).
    (d) The effects of likely fault conditions (such as, but not 
limited to, out-of balance, local blockage or enlargement of stator 
vane passages, fuel nozzle blockage, incorrectly scheduled compressor 
variables, etc.) on vibration characteristics, shall be evaluated by 
test or analysis, or by reference to previous experience and shall be 
shown not to create a hazardous condition.
    (e) The vibration stresses associated with the vibration 
characteristics determined under this section must be less than the 
endurance limits of the materials concerned, after making due allowance 
for operating conditions and permitted variations in properties of the 
materials. The suitability of these stress margins must be justified 
for each part evaluated. If it is determined that certain operating 
conditions, or ranges, need to be limited, operating and installation 
limitations shall be established.
    (f) Compliance with this section shall be substantiated for each 
specific installation configuration that can affect the vibration 
characteristics of the engine. If these vibration effects cannot be 
fully investigated during engine certification, the methods by which 
they can be evaluated and methods by which compliance can be shown 
shall be substantiated and defined in the installation documents 
required by Sec. 33.5.
    5. Section 33.92 is revised to read as follows:


Sec. 33.92   Rotor locking tests.

    If windmilling is prevented by a means to lock the rotor(s), the 
engine must be subjected to a test that includes 25 operations of this 
means under the following conditions:
    (a) The engine must be shut down from rated maximum continuous 
thrust or power, and
    (b) The means for stopping and locking the rotor(s) must be 
operated as specified in the engine operating instructions while being 
subjected to the maximum torque that could result from continued flight 
in this condition; and
    (c) Following rotor locking, the rotor(s) must be held stationary 
under these conditions for five minutes for each of the 25 operations.

    Issued in Washington, DC, on February 22, 1995.
Daniel P. Salvano,
Acting Director of Aircraft Certification Service.
[FR Doc. 95-5419 Filed 3-3-95; 8:45 am]
BILLING CODE 4910-13-M