[Federal Register Volume 75, Number 79 (Monday, April 26, 2010)]
[Proposed Rules]
[Pages 21523-21527]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2010-9588]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 33

[Docket No. FAA-2010-0398; Notice No. 10-06]
RIN 2120-AJ62


Airworthiness Standards; Rotor Overspeed Requirements

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: The FAA proposes to amend the aircraft turbine engine rotor 
overspeed type certification standards. This action would establish 
uniform rotor overspeed design and test requirements for aircraft 
engines and turbochargers certificated by the FAA and the European 
Aviation Safety Agency (EASA). The proposed rule would also establish 
uniform standards for the design and testing of engine rotor parts in 
the United States and in Europe, eliminating the need to comply with 
two differing sets of requirements. The proposed rule would improve 
safety by clarifying existing overspeed requirements for aircraft 
turbine engine rotor parts.

DATES: Send your comments on or before July 26, 2010.

ADDRESSES: You may send comments identified by docket number FAA-2010-
0398 using any of the following methods:
     Federal eRulemaking Portal: Go to http://www.regulations.gov and follow the online instructions for sending your 
comments electronically.
     Mail: Send Comments to Docket Operations, M-30; U.S. 
Department of Transportation, 1200 New Jersey Avenue, SE., West 
Building Ground Floor, Room W12-140, Washington, DC 20590-0001.
     Hand Delivery: Take comments to Docket Operations in Room 
W12-140 of the West Building Ground Floor at 1200 New Jersey Avenue, 
SE., Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, 
except Federal holidays.
     Fax: 1-202-493-2251.

For more information on the rulemaking process, see the SUPPLEMENTARY 
INFORMATION section of this document.
    Privacy: We will post all comments we receive, without change, to 
http://www.regulations.gov, including any personal information you 
provide. Using the search function of our docket Web site, anyone can 
find and read the comments received into any of our dockets, including 
the name of the individual sending the comment (or signing the comment 
for an association, business, labor union, etc.). You may review DOT's 
complete Privacy Act Statement in the Federal Register published on 
April 11, 2000 (65 FR 19477-78) or you may visit http://DocketsInfo.dot.gov.
    Docket: To read background documents or comments received, go to 
http://www.regulations.gov at any time and follow the online 
instructions for accessing the docket or go to Docket Operations in 
Room W12-140 of the West Building Ground Floor at 1200 New Jersey 
Avenue, SE., Washington, DC, between 9 a.m. and 5 p.m., Monday through 
Friday, except Federal holidays.

FOR FURTHER INFORMATION CONTACT: For technical questions concerning 
this proposed rule, contact Tim Mouzakis, Engine and Propeller 
Directorate Standards Staff, ANE-111, Engine and Propeller Directorate, 
Federal Aviation Administration, 12 New England Executive Park, 
Burlington, Massachusetts 01803-5299; telephone (781) 238-7114; fax 
(781) 238-7199; e-mail [email protected]. For legal questions 
concerning this proposed rule contact Vincent Bennett, ANE-7, Office of 
Regional Counsel, Federal Aviation Administration, 12 New England 
Executive Park, Burlington, Massachusetts 01803-5299; telephone (781) 
238-7044; fax (781) 238-7055; e-mail [email protected].

SUPPLEMENTARY INFORMATION: Later in this preamble under the Additional 
Information section, we discuss how you can comment on this proposal 
and how we will handle your comments. Included in this discussion is 
related information about the docket, privacy, and the handling of 
proprietary or confidential business information. We also discuss how 
you can get a copy of

[[Page 21524]]

this proposal and related rulemaking documents.

Authority for This Rulemaking

    The FAA's authority to issue rules regarding aviation safety is 
found in Title 49 of the United States Code. Subtitle I, Section 106 
describes the authority of the FAA Administrator. Subtitle VII, 
Aviation Programs, describes in more detail the scope of the agency's 
authority.
    We are issuing this rulemaking under the authority described in 
Subtitle VII, Part A, Subpart III, Section 44701, ``General 
requirements.'' Under that section, Congress charges the FAA with 
promoting safe flight of civil aircraft in air commerce by prescribing 
regulations for practices, methods, and procedures the Administrator 
finds necessary for safety in air commerce, including minimum safety 
standards for aircraft engines. This proposed rule is within the scope 
of that authority because it updates existing regulations for rotor 
overspeed for aircraft turbine engines.

Background

    Part 33 of Title 14 of the Code of Federal Regulations prescribes 
aircraft engine airworthiness certification standards for products 
certified in the United States. The Certification Specifications for 
Engines (CS-E) prescribe the corresponding airworthiness standards for 
products certified in Europe by the European Aviation Safety Agency. 
While part 33 and CS-E are similar, they differ in several respects.
    The FAA tasked the Aviation Rulemaking Advisory Committee through 
its Engine Harmonization Working Group to review existing regulations 
and recommend changes that would eliminate differences between the U.S. 
and European engine certification standards by harmonizing to the 
higher standards. This proposed rule is a result of this harmonization 
effort.
    This proposed rule would harmonize rotor overspeed requirements 
found in 14 CFR part 33 with EASA CS-E specifications in CS-E 840, 
Rotor Integrity. The proposed rule would improve safety by establishing 
one harmonized standard requiring:
    (1) Rotors be designed with a burst/failure speed that exceeds the 
certified operating speeds;
    (2) Burst speeds to exceed overspeed conditions that can result 
from the failure of other engine components; and
    (3) Limits on the amount of rotor growth or damage that results 
from an overspeed.

Definition of Terms Used in the Rule

    For the purposes of the rule, the following definitions, which are 
consistent with part 33 and CS-E, apply:
    Maximum permissible rotor speed. The maximum approved rotor speed, 
including transients, for the maximum approved rating, including One-
Engine-Inoperative (OEI) ratings.
    Overspeed Capability. The r.p.m. (revolutions per minute) at which 
the part fails or bursts.
    Rotor Growth. The permanent increase in a rotor part's radial 
dimensions caused by an overspeed condition.

General Discussion of the Proposal

    The proposed rule would require that rotor parts be designed with a 
safety margin large enough that the parts have an overspeed capability 
that exceeds the engine's certified operating conditions, including 
overspeed conditions which can occur in the event of a failure of 
another engine component and/or system malfunction. For failures that 
may result in an overspeed, the proposed rule would limit rotor growth 
to that which would not lead to a hazardous condition as defined by 
Sec.  33.75.
    The proposed rule would harmonize U.S. requirements with EASA's by:
     Changing the current FAA overspeed design margin from 115 
to 120 percent of maximum permissible speed for all engine ratings 
except OEI ratings of less than 2\1/2\ minutes;
     Changing the current FAA overspeed design margin from100 
to 105 percent for operating conditions associated with multiple 
failures;
     Introducing similar OEI overspeed design requirements;
     Requiring new similar rotor pass/fail design criteria;
     Requiring similar overspeed margin requirements;
     Allowing the use of validated structural analysis tools to 
demonstrate compliance;
     Requiring that validated structural analysis tools be 
calibrated to actual overspeed tests of similar rotors; and
     Allowing engine test durations of less than 5 minutes for 
failure conditions for which a 5-minute duration is not realistic.
    Like EASA's CS-E, the proposed rule would specify that rotors may 
not burst for overspeed conditions that do not involve component or 
system failure. For component or engine failures that result in an 
overspeed, the proposed rule specifies that rotors may not burst and 
limits the amount of rotor growth.

Overspeed Test Requirements

    The current rule allows the rotor part being tested to be selected 
at random and does not require the test speed to be adjusted to ensure 
a minimum specification rotor can achieve the required overspeed. The 
proposed rule would allow the test speed to be adjusted/increased to 
account for the most adverse combination of material properties and 
dimensional tolerances. This proposed change harmonizes our overspeed 
test requirements with CS-E 840(a) and (d).
    Single or multiple failures of components and/or systems can result 
in an overspeed that is sudden, transient and continues for a brief 
period of time. In this situation, the FAA considers it unrealistic to 
require an engine test that is attempting to duplicate these types of 
failures to maintain an overspeed beyond that which can be expected to 
occur. Under the proposed rule, the FAA would accept the actual 
overspeed duration provided the required maximum rotor speed is 
achieved.

Overspeed Requirements for OEI Ratings

    The current rule does not specify the overspeed requirements for 
one-engine inoperative ratings and assumes overspeed requirements are 
the same for any engine rating. The current rule requires an overspeed 
margin of 115 percent of the maximum permissible speed if tested in an 
engine. The proposed rule requires an overspeed margin of 120 percent 
for all ratings, except for 115 percent for OEI ratings less than 2\1/
2\ minutes. The proposed change to overspeed requirements for OEI 
ratings would harmonize with CS-E 840(b).

Overspeed Events Due to Failure of Components or Systems

    The current rule requires a 5 percent overspeed margin for the 
failure of a single component or system and zero overspeed margin for 
the failure of multiple components. The proposed rule specifies a 5 
percent overspeed margin for both single and combined failure 
situations for all ratings except OEI ratings of less than 2\1/2\ 
minutes.
    When operating at an OEI rating of less than 2\1/2\-minute duration 
and a single failure occurs, the proposed rule requires that rotor 
components be designed and tested to withstand 100 percent of the 
resulting overspeed. The proposed changes to overspeed requirements for 
OEI ratings harmonize with those in CS-E 840(b).

[[Page 21525]]

Exclusion of Certain Shaft Sections From Overspeed Tests

    The current rule in Sec.  33.27(c)(2)(v) requires that all shaft 
locations be considered in determining the terminal rotor speed due to 
failure and be tested to 105 percent of the highest terminal rotor 
speed. The proposed rule in Sec.  33.27(f) would exclude certain shaft 
sections, but not the whole shaft system, from this requirement. The 
FAA finds the proposed rule is consistent with the way the FAA has 
applied the current rule to industry in certification tests. The FAA 
has consistently accepted engineering assessments that support the 
applicant's findings that certain location(s) (sections) of a shaft 
system are considered ``prime reliable,'' which means that these shaft 
locations are not likely to fail during the life of the engine. The FAA 
is, therefore, proposing to change the current rule to be consistent 
with the current certification practices. The proposed changes to 
overspeed requirements due to shaft failures would be consistent with 
those in CS-E-850(b).

Rulemaking Analyses and Notices

Paperwork Reduction Act

    The Paperwork Reduction Act of 1995 (44 U.S.C. 3507(d)) requires 
that the FAA consider the impact of paperwork and other information 
collection burdens imposed on the public. We have determined there is 
no current or new information collection requirements associated with 
this proposed rule.

International Compatibility

    In keeping with U.S. obligations under the Convention on 
International Civil Aviation, it is FAA policy to comply with 
International Civil Aviation Organization (ICAO) Standards and 
Recommended Practices to the maximum extent practicable. We determined 
that no conflict with ICAO Standards and Recommended Practices exists, 
since there are no corresponding ICAO Standards and Recommended 
Practices.

Regulatory Evaluation, Regulatory Flexibility Determination, 
International Trade Impact Assessment, and Unfunded Mandates Assessment

    Proposed changes to Federal regulations must undergo several 
economic analyses. 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 (Pub. L. 96-354) 
requires agencies to analyze the economic impact of regulatory changes 
on small entities. Third, the Trade Agreements Act (Pub. L. 96-39) 
prohibits agencies from setting standards that create unnecessary 
obstacles to the foreign commerce of the United States. In developing 
U.S. standards, this Trade Act requires agencies to consider 
international standards and, where appropriate, that they be the basis 
of U.S. standards. Fourth, the Unfunded Mandates Reform Act of 1995 
(Pub. L. 104-4) requires agencies to prepare a written assessment of 
the costs, benefits, and other effects of proposed or final rules that 
include a Federal mandate likely to result in the expenditure by State, 
local, or tribal governments, in the aggregate, or by private sector, 
of $100 million or more annually (adjusted for inflation with base year 
of 1995). This portion of the preamble contains the FAA's analysis of 
the economic impacts of this proposed rule.
    In conducting these analyses, the FAA has determined that this 
proposed rule: (1) Has benefits that justify its costs, (2) is not an 
economically ``significant regulatory action'' as defined in section 
3(f) of Executive Order 12866, (3) is not ``significant'' as defined in 
DOT's Regulatory Policies and Procedures; (4) would not have a 
significant economic impact on a substantial number of small entities; 
(5) would not create unnecessary obstacles to the foreign commerce of 
the United States; and (6) would not impose an unfunded mandate on 
State, local, or tribal governments, or on the private sector by 
exceeding the threshold identified above.

Total Estimated Benefits and Costs of This Proposed Rule

    Presently, turbine aircraft engine manufacturers must satisfy both 
FAA part 33 and EASA CS-E regulations to certify their products in the 
United States and Europe. Certification to one standard would improve 
certification efficiency by eliminating duplicate testing and 
documentation. We have not attempted to quantify the cost savings that 
may accrue due to this improved certification efficiency beyond noting 
that these are expected to be minor. We have drawn that conclusion 
based on the consensus among potentially affected aircraft engine 
manufacturers.
    Industry must currently certificate to the two standards that are 
substantively similar, but have a few slightly different testing and 
documentation procedures and requirements. The proposed rule would 
harmonize these procedures and requirements to the higher standard and, 
thereby, may increase safety. In addition, by reducing the amount of 
duplicative testing that would need to be either witnessed or analyzed 
by the FAA, the FAA would be better able to prioritize its resources to 
other, more safety critical areas. Consequently, the FAA determines 
there could be unquantifiable future minimal benefits from the proposed 
rule.
    As a result, the FAA concludes that the combination of cost savings 
and potential increased safety benefits would make this proposed rule 
cost beneficial.
    The FAA requests comments on these estimates of potential cost 
savings and benefits from this proposed rule.
    The FAA has, therefore, determined that this proposed rule is not a 
``significant regulatory action'' as defined in section 3(f) of 
Executive Order 12866, and is not ``significant'' as defined in DOT's 
Regulatory Policies and Procedures.

Regulatory Flexibility Determination

    The Regulatory Flexibility Act of 1980 (Pub. L. 96-354) (RFA) 
establishes ``as a principle of regulatory issuance that agencies shall 
endeavor, consistent with the objectives of the rule and of applicable 
statutes, to fit regulatory and informational requirements to the scale 
of the businesses, organizations, and governmental jurisdictions 
subject to regulation. To achieve this principle, agencies are required 
to solicit and consider flexible regulatory proposals and to explain 
the rationale for their actions to assure that such proposals are given 
serious consideration.'' The RFA covers a wide-range of small entities, 
including small businesses, not-for-profit organizations, and small 
governmental jurisdictions.
    Agencies must perform a review to determine whether a rule will 
have a significant economic impact on a substantial number of small 
entities. If the agency determines that it will, the agency must 
prepare a regulatory flexibility analysis as described in the RFA.
    However, if an agency determines that a rule is not expected to 
have a significant economic impact on a substantial number of small 
entities, section 605(b) of the RFA provides that the head of the 
agency may so certify and a regulatory flexibility analysis is not 
required. The certification must include a statement providing the 
factual basis for this determination, and the reasoning should be 
clear.
    The net effect of this proposed rule would provide regulatory cost 
relief. Second, all but one U.S. aircraft turbine engine manufacturer 
exceeds the Small

[[Page 21526]]

Business Administration small-entity criteria for aircraft engine 
manufacturers of 1,500 employees. U.S. transport category aircraft 
engine manufacturers include: General Electric (GE); CFM International 
(a joint company of GE and Snecma); Pratt & Whitney (P&W); Honeywell; 
Rolls-Royce Corporation (formerly Allison Engines); International Aero 
Engines (a privately-held consortium that includes P&W, Rolls-Royce, 
Japanese Aero Engines Corporation, and MTU Aero Engines); and Williams 
International. Williams International is the only one of these 
manufacturers that is categorized as a U.S. small business by the SBA 
criteria. This proposed rule would reduce costs, and there is only one 
small entity manufacturing part 33 aircraft engines. Therefore, the FAA 
certifies that this action would not have a significant economic impact 
on a substantial number of small entities. The FAA solicits comments 
regarding this determination.

International Trade Impact Assessment

    The Trade Agreements Act of 1979 (Pub. L. 96-39), as amended by the 
Uruguay Round Agreements Act (Pub. L. 103-465), prohibits Federal 
agencies from establishing standards or engaging in related activities 
that create unnecessary obstacles to the foreign commerce of the United 
States. Pursuant to these Acts, the establishment of standards is not 
considered an unnecessary obstacle to the foreign commerce of the 
United States, so long as the standard has a legitimate domestic 
objective, such as protection of safety, and does not operate in a 
manner that excludes imports that meet this objective. The statute also 
requires consideration of international standards and, where 
appropriate, that they be the basis for U.S. standards. The FAA 
assessed the potential effect of this proposed rule and determined that 
it uses European standards as the basis for regulation and thus is 
consistent with the Trade Assessments Act.

Unfunded Mandates Assessment

    Title II of the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-
4) requires each Federal agency to prepare a written statement 
assessing the effects of any Federal mandate in a proposed or final 
agency rule that may result in an expenditure of $100 million or more 
(in 1995 dollars) in any one year by State, local, and tribal 
governments, in the aggregate, or by the private sector; such a mandate 
is deemed to be a ``significant regulatory action.'' The FAA currently 
uses an inflation-adjusted value of $136.1 million in lieu of $100 
million. This proposed rule does not contain such a mandate, therefore, 
the requirements of Title II of the Act do not apply.

Executive Order 13132, Federalism

    The FAA has analyzed this proposed rule under the principles and 
criteria of Executive Order 13132, Federalism. We determined that this 
action would not have a substantial direct effect 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, and therefore would not have federalism implications.

Environmental Analysis

    FAA Order 1050.1E defines FAA actions that are categorically 
excluded from preparation of an environmental assessment or 
environmental impact statement under the National Environmental Policy 
Act (NEPA) in the absence of extraordinary circumstances. The FAA has 
determined this proposed rulemaking action qualifies for the 
categorical exclusion identified in Chapter 3, paragraph 312d, and 
involves no extraordinary circumstances.

Regulations That Significantly Affect Energy Supply, Distribution, or 
Use

    The FAA has analyzed this NPRM under Executive Order 13211, Actions 
Concerning Regulations that Significantly Affect Energy Supply, 
Distribution, or Use (May 18, 2001). We have determined that it is not 
a ``significant energy action'' under the executive order and is not 
likely to have a significant adverse effect on the supply, 
distribution, or use of energy.

Additional Information

Comments Invited
    The FAA invites interested persons to participate in this 
rulemaking by submitting written comments, data, or views. We also 
invite comments relating to the economic, environmental, energy, or 
federalism impacts that might result from adopting the proposals in 
this document. The most helpful comments reference a specific portion 
of the proposal, explain the reason for any recommended change, and 
include supporting data. To ensure the docket does not contain 
duplicate comments, please send only one copy of written comments, or 
if you are filing comments electronically, please submit your comments 
only one time.
    We will file in the docket all comments we receive, as well as a 
report summarizing each substantive public contact with FAA personnel 
concerning this proposed rulemaking. Before acting on this proposal, we 
will consider all comments we receive on or before the closing date for 
comments. We will consider comments filed after the comment period has 
closed if it is possible to do so without incurring expense or delay. 
We may change this proposal in light of the comments we receive.
Proprietary or Confidential Business Information
    Do not file in the docket information that you consider to be 
proprietary or confidential business information. Send or deliver this 
information directly to the person identified in the FOR FURTHER 
INFORMATION CONTACT section of this document. You must mark the 
information that you consider proprietary or confidential. If you send 
the information on a disk or CD-ROM, mark the outside of the disk or 
CD-ROM and also identify electronically within the disk or CD-ROM the 
specific information that is proprietary or confidential.
    Under 14 CFR 11.35(b), when we are aware of proprietary information 
filed with a comment, we do not place it in the docket. We hold it in a 
separate file to which the public does not have access, and we place a 
note in the docket that we have received it. If we receive a request to 
examine or copy this information, we treat it as any other request 
under the Freedom of Information Act (5 U.S.C. 552). We process such a 
request under the DOT procedures found in 49 CFR part 7.

Availability of Rulemaking Documents

    You can get an electronic copy using the Internet by--
    (1) Searching the Federal eRulemaking Portal (http://www.regulations.gov);
    (2) Visiting the FAA's Regulations and Policies Web page at http://www.faa.gov/regulations_policies/; or
    (3) Accessing the Government Printing Office's Web page at http://www.gpo.gov/fdsys/search/home.action.
    You can also get a copy by sending a request to the Federal 
Aviation Administration, Office of Rulemaking, ARM-1, 800 Independence 
Avenue, SW, Washington, DC 20591, or by calling (202) 267-9680. Make 
sure to identify the docket number or notice number of this rulemaking.
    You may access all documents the FAA considered in developing this 
proposed rule, including economic analyses and technical reports, from 
the Internet through the Federal eRulemaking Portal referenced in 
paragraph (1).

[[Page 21527]]

List of Subjects in 14 CFR Part 33

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    In consideration of the foregoing, the Federal Aviation 
Administration proposes to amend Chapter I of Title 14, Code of Federal 
Regulations 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. Revise Sec.  33.27 to read as follows:


Sec.  33.27  Turbine, compressor, fan, and turbosupercharger rotor 
overspeed.

    (a) For each fan, compressor, turbine, and turbosupercharger rotor, 
the applicant must establish by test, analysis, or a combination of 
both, that each rotor will not burst when operated in the engine for 5 
minutes at whichever of the conditions defined in paragraph (b) of this 
section is the most critical with respect to the integrity of such a 
rotor.
    (1) Test rotors used to demonstrate compliance with this section 
that do not have the most adverse combination of material properties 
and dimensional tolerances must be tested at conditions which have been 
adjusted to ensure the minimum specification rotor possesses the 
required overspeed capability. This can be accomplished by increasing 
test speed, temperature, and/or loads.
    (2) When an engine test is being used to demonstrate compliance 
with the overspeed conditions listed in paragraph (b)(3) or (b)(4) of 
this section and the failure of a component or system is sudden and 
transient, it may not be possible to operate the engine for 5 minutes 
after the failure. Under these circumstances, the actual overspeed 
duration is acceptable if the required maximum overspeed is achieved.
    (b) When determining the maximum overspeed condition applicable to 
each rotor in order to comply with paragraphs (a) and (c) of this 
section, the applicant must evaluate the following rotor speeds taking 
into consideration the part's operating temperatures and temperature 
gradients throughout the engine's operating envelope:
    (1) 120 percent of the maximum permissible rotor speed associated 
with any of the engine ratings except one-engine-inoperative (OEI) 
ratings of less than 2\1/2\ minutes.
    (2) 115 percent of the maximum permissible rotor speed associated 
with any OEI ratings of less than 2\1/2\ minutes.
    (3) 105 percent of the highest rotor speed that would result from 
either:
    (i) The failure of the component or system which, in a 
representative installation of the engine, is the most critical with 
respect to overspeed when operating at any rating condition except OEI 
ratings of less than 2\1/2\ minutes, or
    (ii) The failure of any component or system in a representative 
installation of the engine, in combination with any other failure of a 
component or system that would not normally be detected during a 
routine pre-flight check or during normal flight operation, that is the 
most critical with respect to overspeed, except as provided by 
paragraph (c) of this section, when operating at any rating condition 
except OEI ratings of less than 2\1/2\ minutes.
    (4) 100 percent of the highest rotor speed that would result from 
the failure of the component or system which, in a representative 
installation of the engine, is the most critical with respect to 
overspeed when operating at any OEI rating of less than 2\1/2\ minutes.
    (c) The highest overspeed that results from a complete loss of load 
on a turbine rotor, except as provided by paragraph (f) of this 
section, must be included in the overspeed conditions considered by 
paragraphs (b)(3)(i), (b)(3)(ii), and (b)(4) of this section, 
regardless of whether that overspeed results from a failure within the 
engine or external to the engine. The overspeed resulting from any 
other single failure must be considered when selecting the most 
limiting overspeed conditions applicable to each rotor. Overspeeds 
resulting from combinations of failures must also be considered unless 
the applicant can show that the probability of occurrence is not 
greater than 10-9 per flight.
    (d) In addition, the applicant must demonstrate that each fan, 
compressor, turbine, and turbosupercharger rotor complies with 
paragraphs (d)(1) and (d)(2) of this section for the maximum overspeed 
achieved when subjected to the conditions specified in paragraphs 
(b)(3) and (b)(4) of this section. The applicant must use the approach 
in paragraph (a) of this section which specifies the required test 
conditions.
    (1) Rotor Growth must not cause the engine to:
    (i) Catch fire,
    (ii) Release hazardous fragments through the engine casing or 
result in a hazardous failure of the engine casing,
    (iii) Generate loads greater than those ultimate loads specified in 
Sec.  33.23(a), or
    (iv) Lose the capability of being shut down.
    (2) Following an overspeed event and after continued operation, the 
rotor may not exhibit conditions such as cracking or distortion which 
preclude continued safe operation.
    (e) The design and functioning of engine control systems, 
instruments, and other methods not covered under Sec.  33.28 must 
ensure that the engine operating limitations that affect turbine, 
compressor, fan, and turbosupercharger rotor structural integrity will 
not be exceeded in service.
    (f) Failure of a shaft section may be excluded from consideration 
in determining the highest overspeed that would result from a complete 
loss of load on a turbine rotor if the applicant:
    (1) Identifies the shaft as an engine life-limited-part and 
complies with Sec.  33.70.
    (2) Uses material and design features that are well understood and 
that can be analyzed by well-established and validated stress analysis 
techniques.
    (3) Determines, based on an assessment of the environment 
surrounding the shaft section, that environmental influences are 
unlikely to cause a shaft failure. This assessment must include 
complexity of design, corrosion, wear, vibration, fire, contact with 
adjacent components or structure, overheating, and secondary effects 
from other failures or combination of failures.
    (4) Identifies and declares, in accordance with Sec.  33.5, any 
assumptions regarding the engine installation in making the assessment 
described above in paragraph (f)(3) of this section.
    (5) Assesses, and considers as appropriate, experience with shaft 
sections of similar design.
    (6) Does not exclude the entire shaft.
    (g) If analysis is used to meet the overspeed requirements, then 
the analytical tool must be calibrated to prior overspeed test results 
of a similar rotor. The tool must be calibrated for the same material, 
rotor geometry, stress level, and temperature range as the rotor being 
certified. Calibration includes the ability to accurately predict rotor 
dimensional growth and the burst speed. The predictions must also show 
that the rotor being certified does not have lower burst and growth 
margins than rotors used to calibrate the tool.

    Issued in Washington, DC, on April 20, 2010.
Dorenda D. Baker,
Director, Aircraft Certification Service.
[FR Doc. 2010-9588 Filed 4-23-10; 8:45 am]
BILLING CODE 4910-13-P