[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]]


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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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