[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]]
_______________________________________________________________________
Part VIII
Department of Transportation
_______________________________________________________________________
Federal Aviation Administration
_______________________________________________________________________
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]
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