[Federal Register Volume 61, Number 108 (Tuesday, June 4, 1996)]
[Rules and Regulations]
[Pages 28430-28433]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-13946]
[[Page 28429]]
_______________________________________________________________________
Part V
Department of Transportation
_______________________________________________________________________
Federal Aviation Administration
_______________________________________________________________________
14 CFR Part 33
Airworthiness Standards; Continued Rotation and Rotor Locking Tests,
and Vibration and Vibration Tests; Final Rule
Federal Register / Vol. 61, No. 108 / Tuesday, June 4, 1996 / Rules
and Regulations
[[Page 28430]]
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 33
[Docket No. 28107; Amendment No. 33-17]
RIN 2120-AF57
Airworthiness Standards; Continued Rotation and Rotor Locking
Tests, and Vibration and Vibration Tests
AGENCY: Federal Aviation Administration, DOT.
ACTION: Final rule.
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SUMMARY: This amendment revises the Federal Aviation Administration's
(FAA's) continued rotation and vibration certification standards for
the issuance of original and amended type certificates for aircraft
engines. This amendment is the result of an effort to harmonize the
Federal Aviation Regulations (FAR's) with European requirements being
drafted by the Joint Aviation Authorities (JAA). This amendment will
provide nearly uniform requirements that will simplify international
airworthiness approval, while maintaining a level of safety equivalent
to that established by the current standards.
DATES: Effective July 5, 1996.
FOR FURTHER INFORMATION CONTACT:
Marc Bouthillier, 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, MA 01803-5299; telephone (617) 238-7111;
fax (617) 238-7199.
SUPPLEMENTARY INFORMATION:
Background
Part 33 of title 14 of the Code of Federal Regulations (14 CFR part
33) prescribes certification standards for the issuance of original and
amended type certificates for aircraft engines. Part E of the Joint
Aviation Requirements (JAR-E) prescribes the corresponding
certification standards of the 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 continued rotation and rotor locking
test requirements, and vibration and vibration test requirements, were
identified as differences sufficiently significant to cause the JAA to
apply additional conditions to U.S. manufacturers seeking JAA
certification. The FAA requested the ARAC to further evaluate these
initiatives and ARAC assigned the task to the Propulsion Harmonization
Working Group. The task resulted in an ARAC recommendation to the FAA
to proceed with rulemaking. The FAA issued a Notice of Proposed
Rulemaking (NPRM), No. 95-3, published in the Federal Register (60 FR
12360, dated March 6, 1995). The proposal reflected the ARAC
recommendations.
Discussion of Comments
All interested persons have been afforded an opportunity to
participate in this rulemaking, and due consideration has been given to
all comments received. The commenters represent domestic industry and
foreign airworthiness authorities. Six commenters provided the FAA with
comments to NPRM 95-3. Two of these six commenters expressed no
objection to the proposals. The comments are grouped according to the
applicable revised and new sections of part 33.
Section 33.74 Continued Rotation
Two commenters state that the term ``windmilling'' should be
changed to ``continued rotation,'' to be consistent with the existing
wording of part 23 and part 25, and to encompass mechanical as well as
aerodynamic effects.
The FAA agrees. The FAA has changed the term ``windmilling'' to
``continued rotation,'' wherever it appears.
One commenter states that the wording of proposed 33.74 in the NPRM
is awkward, and should be revised for clarity.
The FAA agrees. The FAA has rewritten this section to more clearly
state the requirement. The phrase ``any of the engine main rotating
systems'' replaces ``engine'', and the revised section now specifies
that the standard does not apply when rotor locking systems are in
place. In addition the phrase ``and in the flight conditions expected
to occur'' replaces the phrase ``likely to occur''. The FAA has also
made additional changes to revised Sec. 33.74 as noted in response to
other comments.
One commenter states that the term ``typical installation'' should
be deleted, because the rule applies to all installations.
The FAA agrees. This term has been deleted from this section.
One commenter states that the term ``for any reason'' be either
deleted or clarified, because this wording will require compliance for
the case of a failed rotor locking devices, if installed.
The FAA agrees. The rule does not intend to consider a failed rotor
locking device. The FAA has, therefore, added a clarifying statement to
this effect. However, the term ``for any reason'' has been retained to
cover all other reasons for an engine shutdown.
One commenter states that the term ``flight conditions expected to
occur'' be included in the text of the rule.
The FAA agrees. The FAA has included this term in the rule.
Two commenters state that the term ``hazard to the aircraft''
should be deleted, and replaced by more definitive criteria.
The FAA agrees. The FAA has replaced this term with a more
definitive criteria by referencing Sec. 33.75. That criteria can be
evaluated at the engine level, without the need for an aircraft
installation assessment.
One commenter states that the proposed rule should also require
determination of aircraft/engine interface loads associated with
continued rotation with rotor unbalance, and submittal of these for
engine certification.
The FAA disagrees. The FAA considers this comment to be beyond the
scope of this rulemaking, because the proposal addresses only the
continued rotation characteristics of the engine; it did not address
aircraft structural requirements for various engine load conditions.
Also, the commenter does not specify any criteria for evaluating
aircraft/engine interface loads, which can only be evaluated when
considering an entire airplane.
Section 33.63 Vibration
One commenter expressed concern with the apparent inference to
structural assessments of the aircraft due to engine dynamic loads. The
commenter suggests that this part of the proposal not be issued and
that the appropriate ARAC Structures and Propulsion working groups be
tasked to work the issue.
The FAA disagrees. The FAA considers this comment is beyond the
scope of this rulemaking. The revision
[[Page 28431]]
to Sec. 33.63 clarifies, but does not alter, the original intent of a
requirement that was promulgated as a Civil Air Regulation on June 15,
1956. The practical application of this requirement is to demonstrate
those peak vibratory stresses of engine components do not exceed the
material endurance limit for all normal engine operation (i.e., does
not consider engine failure conditions that would be evident to the
crew). The requirement of parts 23.939, 25.939, 27.939, and 29.939
further ensures that the installation of the engine to the aircraft
will not result in excessive vibratory stresses of engine components
for all normal engine operation. Additionally, the combined
requirements of paragraphs 33.63 and 33.29(b) require that an
indication of excessive vibration (rotor unbalance) be provided to the
installer. These indications are provided to the crew to alert them of
conditions beyond what is considered normal engine operation so that
immediate corrective actions can be taken. It has never been the intent
of this requirement nor is it the intent of the revised requirement to
establish the abnormal engine environment for designing aircraft
structures. In a separate and unrelated task, the FAA has chartered the
ARAC Loads and Dynamic Harmonization Working Group to assess whether
the current aircraft structural requirements adequately address the
engine dynamic loads resulting from turbine engine failures.
Section 33.83 Vibration test
Section 33.83(a)
One commenter states that additional clarification be provided on
the intended means of measuring vibration stresses. The commenter
states that the requirements infer direct measurements of vibratory
stresses can only be measured using strain gauges.
The FAA disagrees. Typically, vibration stresses are measured
directly. However, in certain instances, indirect measurements of blade
deflections can supplement direct measurements of vibratory stresses.
Further clarification of the intended measurements is not needed as the
regulation retains language that is understood by engine manufacturers
and is basically unchanged since its inception as a Civil Air
Regulation on June 15, 1956.
Section 33.83(b)
One commenter suggested editorial changes to emphasize that the
vibration surveys cover the ranges of physical and corrected rotation
speeds.
The FAA agrees. The paragraph has been revised to better define the
intent of the harmonized vibration requirements.
One commenter states the phrase ``throughout the declared flight
envelope'' was used redundantly in proposed paragraphs 33.83(a) and
33.83(b).
The FAA disagrees. Revised paragraph 33.83(a) contains general
vibration test requirements while revised paragraph 33.83(b) contains
more specific test requirements. The defining term ``throughout the
declared flight envelope'' is needed in both paragraphs.
One commenter states that alternative wording is needed to the
speed extension requirements of proposed paragraph 33.83(b). The
commenter further states that the surveys should be extended
sufficiently to reveal the maximum stress value but limiting the
rotational speed extension to no more than an additional 2 percentage
points.
The FAA agrees. The FAA will incorporate the wording recommended by
the commenter to better define the intent of the speed extension
requirement.
Section 33.83(c)
One commenter states that the proposal eliminates those
requirements specific to accessory drives and mounting attachments, and
also asks whether the FAA is still concerned about accessory drives and
mounting attachments.
The FAA disagrees. The FAA still has concerns on the integration
requirements of accessory drives and mounting attachments and specific
reference to accessory loading is retained in revised paragraph
33.83(c). New paragraph 33.83(f) provides for a more complete and
thorough integration of the engine to the aircraft, including accessory
drives and mounting attachments.
One commenter states that an additional subparagraph to paragraph
33.83(c) is needed to emphasize the requirement to evaluate factors
that might induce or influence flutter vibration.
The FAA agrees. Flutter vibration was included in the discussion of
proposed 33.83(b) in the NPRM. Revised 33.83(c) contains a new
paragraph (c)(2) that defines the intent of the harmonized vibration
requirements.
Section 33.83(d)
Two commenters state that proposed paragraphs 33.83 (d) and (e)
need clarification to distinguish between the standard that applies to
normal operation from that applicable to likely fault conditions. One
suggests that the order of proposed paragraphs 33.83 (d) and (e) needs
to be reversed.
The FAA agrees. The FAA has reversed order of new paragraphs 33.83
(d) and (e) and has added additional words to clarify which criterion
applies in each condition.
One commenter suggested editorial changes to clarify that vibratory
stresses are combined with steady stresses when comparing to the
material's endurance limit.
The FAA agrees. The paragraph has been revised to better define the
intent of the harmonized vibration requirements. The phrase ``when
combined with the appropriate steady state stresses'' has been added to
new paragraph 33.83(d).
One commenter states that proposed paragraph 33.83(e) appears to be
a design not a performance requirement, and therefore, infers that this
proposed paragraph is inappropriately included in the vibration test
section.
The FAA disagrees. New paragraph 33.83(d) is the primary criterion
for evaluating the results of tests and analyses conducted in
accordance with revised paragraphs 33.83 (a), (b), and (c).
One commenter states that the standard requiring vibration stresses
to be less than the endurance limits of the materials concerned should
be relaxed to assess the vibration stresses against the endurance
limits of the materials concerned.
The FAA does not agree. The commenter's suggestion allows for
acceptance of vibration stresses greater than the endurance limits
without any definitive limitation. All engines on an aircraft are
subject to the same environmental and operating conditions. The
standard requiring vibratory stresses of less than the endurance limit
is necessary, therefore, to minimize the likelihood of having multiple
engines on the same aircraft fail for the same root cause. The FAA
recognizes that there may be instances where a particular vibration
failure mode does not result in engine anomalies (such as, power loss,
high vibrations sensed by the flight crew, limit exceeded) that could
cascade into a hazardous condition. The FAA has determined that such
instances are rare. The FAA can evaluate the merit of these instances
on a case by case basis.
Section 33.83(e)
One commenter suggested editorial changes to clarify the assessment
of fault conditions.
The FAA agrees. The paragraph has been revised to better define the
intent of the harmonized vibration requirements. The phrase ``of likely
[[Page 28432]]
fault conditions'' has been replaced by the phrase ``of excitation
forces caused by fault conditions'', and the phrase ``on vibration
characteristics'' has been moved to the beginning of the paragraph.
One commenter states that the requirement to assess vibrations
should not apply throughout the declared flight envelope for failure
conditions. The commenter further states that it is excessive to
require assessments throughout the declared flight envelope for failure
conditions.
The FAA does not agree. The FAA does not intend that the
requirements apply to all failure conditions. No assessments are
required, for example, where the condition will quickly result in an
engine shutdown or result in immediate symptoms that will necessitate
flight crew actions. The FAA does intend, however, that assessments be
made of typical fault conditions (such as, turbine nozzle guide vane
burn-throughs, fuel nozzle blockage, minor foreign object damage) that
may not be immediately detectable by the flight crew and that could
cascade into a hazardous condition. Requiring assessments of typical
fault conditions throughout the declared flight envelope is not
considered excessive. The assessment criterion for fault conditions is
to show only that no hazardous condition is created, where the stricter
assessment criterion for normal operation requires that assessed
vibratory stresses do not exceed the material's endurance limit.
Section 33.83(f)
One commenter suggested changing ``installation documents'' to read
``installation instructions'' to be consistent with Sec. 33.5.
The FAA agrees. The noted editorial change has been incorporated.
Paperwork Reduction Act
In accordance with the Paperwork Reduction Act on 1990 (44 U.S.C.
3501 et seq.), there are no requirements for information collection
associated with this rule.
Regulatory Evaluation, Regulatory Flexibility Determination, and
Trade Impact Assessment
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 effect of regulatory changes on international trade. In conducting
these analyses, the FAA has determined that this rule: (1) will
generate benefits outweighing its costs; (2) is not a ``significant
regulatory action'' as defined in the Executive Order; (3) is not
``significant'' as defined by DOT's policies and procedures; (4) will
not have a significant impact on a substantial number of small
entities; and (5) will not constitute a barrier to international trade.
These analyses, available in the docket, are summarized below.
Regulatory Evaluation Summary
Of the several amendments, only one might result in additional
cost. The FAA has identified the requirements in revised Sec. 33.83(b)
as the only amendment that could require minor additional engine
testing and engineering analysis, resulting in minor additional
compliance costs. The revised engine continued rotation requirements of
new Sec. 33.74 and the amendments to Sec. 33.92(a) could potentially
result in cost savings to engine and transport airplane manufacturers.
The primary benefits of the rule will be harmonization of
airworthiness standards with the European Joint Aviation Requirements
and clarification of existing standards. The resulting increased
uniformity of standards will simplify airworthiness approval for import
and export purposes and will 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 will far exceed the minor incremental cost of the rule.
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 Federal Regulations. The RFA requires a
Regulatory Flexibility Analysis if a proposed rule will have a
significant economic impact, either detrimental or beneficial, on a
substantial number of small entities. Based on FAA Order 2100.14A
(Regulatory Flexibility Criteria and Guidance), which outlines
procedures and criteria for implementing the RFA, the FAA has
determined that the rule will not have a significant economic impact on
a substantial number of small entities.
International Trade Impact Assessment
The rule will 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 U.S. Instead, the
revised standards will harmonize with existing and proposed standards
of foreign aviation authorities, thereby lessening restraints on trade.
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 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 amendments and the foreign regulations.
Federalism Implications
The regulations adopted herein will not have substantial direct
effects on the States, on the relationship between the national
government and the States, or on the distribution of power and
responsibilities among the various levels of government. Therefore, in
accordance with Executive Order 12612, it is determined that this
regulation will not have sufficient federalism implications to warrant
the preparation of a Federalism Assessment.
Conclusion
For the reasons discussed above, the FAA has determined that this
regulation (1) is not a ``significant regulatory action'' under
Executive Order 12866; (2) is not a ``significant rule'' under DOT
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979);
(3) will not have a significant economic impact, positive or negative,
on a substantial number of small entities under the criteria of the
RFA; and (4) will not substantially impact on international trade. A
final regulatory evaluation of the regulation, including a final
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, Safety.
[[Page 28433]]
Adoption of the Amendment
Accordingly, the Federal Aviation Administration (FAA) amends 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. 106(g), 40113, 44701, 44702, 44704.
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 Continued rotation.
If any of the engine main rotating systems will continue to rotate
after the engine is shutdown for any reason while in flight, and where
means to prevent that continued rotation are not provided; then any
continued rotation during the maximum period of flight, and in the
flight conditions expected to occur with that engine inoperative, must
not result in any condition described in Sec. 33.75 (a) through (c).
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 rotational speed up
to 103 percent of the maximum physical and corrected rotational speed
permitted for rating periods of two minutes or longer, and up to 100
percent of all other permitted physical and corrected rotational
speeds, including those that are overspeeds. If there is any indication
of a stress peak arising at the highest of those required physical or
corrected rotational speeds, the surveys shall be extended sufficiently
to reveal the maximum stress values present, except that the extension
need not cover more than a further 2 percentage points increase beyond
those speeds.
(c) Evaluations shall be made of the following:
(1) 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); and
(2) The aerodynamic and aeromechanical factors which might induce
or influence flutter in those systems susceptible to that form of
vibration.
(d) Except as provided by paragraph (e) of this section, the
vibration stresses associated with the vibration characteristics
determined under this section, when combined with the appropriate
steady stresses, must be less than the endurance limits of the
materials concerned, after making due allowances for operating
conditions for the 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.
(e) The effects on vibration characteristics of excitation forces
caused by fault conditions (such as, but not limited to, out-of
balance, local blockage or enlargement of stator vane passages, fuel
nozzle blockage, incorrectly schedule compressor variables, etc.) shall
be evaluated by test or analysis, or by reference to previous
experience and shall be shown not to create a hazardous condition.
(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 instructions
required by Sec. 33.5.
5. Section 33.92 is revised to read as follows:
Sec. 33.92 Rotor locking tests.
If continued rotation 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 May 29, 1996.
David R. Hinson,
Administrator.
[FR Doc. 96-13946 Filed 6-3-96; 8:45 am]
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