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Airworthiness Standards; Aircraft Engine Standards Overtorque Limits

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Start Preamble


Federal Aviation Administration (FAA), DOT.


Final rule.


This rule will amend the certification standards for aircraft engines to establish requirements for approval of maximum engine overtorque. Specifically, this action will add a new engine overtorque test, amend engine ratings and operating limits, and define maximum engine overtorque for certain turbopropeller and turboshaft engines. The rule will Start Printed Page 45308harmonize applicable United States (U.S.) and European standards and simplify airworthiness approvals for import and export of aircraft engines.


This amendment becomes effective November 2, 2009.

Start Further Info


For technical questions concerning this final rule contact Tim Mouzakis, Engine and Propeller Directorate, Standards Staff, ANE-110, Federal Aviation Administration (FAA), New England Region, 12 New England Executive Park, Burlington, Massachusetts 01803; telephone (781) 238-7114; facsimile (781) 238-7199; electronic mail “”

End Further Info End Preamble Start Supplemental Information


Authority for This Rulemaking

The FAA's authority to issue rules on 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.

This rulemaking is promulgated under the authority described in subtitle VII, part A, subpart III, section 44701, “General requirements.” Under that section, the FAA is charged 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 regulation is within the scope of that authority because it updates the existing regulations for aircraft engine standards overtorque limits.


Part 33 of Title 14, Code of Federal Regulations (14 CFR part 33) prescribes airworthiness standards for original and amended type certificates for aircraft engines. The European Aviation Safety Agency (EASA) Certification Specification—Engines (CS-E) prescribes corresponding airworthiness standards to certify aircraft engines in Europe. While part 33 and the CS-E are similar, they differ in several respects. These differences result in added costs, delays, and time required for certification. In addition, U.S. aircraft engine manufacturers face additional costs when seeking certification of their engine designs by the EASA for export. CS-E contains specific standards for approval of maximum overtorque limits.

Currently, part 33 does not contain explicit standards for a maximum engine overtorque limit. Engine manufacturers apply for and obtain FAA approvals of maximum overtorque limits based on the results of certification engine tests and analysis that do not directly address considerations for maximum overtorque limits.

The FAA tasked the Aviation Rulemaking Advisory Committee (ARAC), through its Engine Harmonization Working Group (EHWG), to provide advice and recommendations on proposed standards for engine overtorque. We published that tasking in the Federal Register on October 20, 1998 (63 FR 56059). This final rule is based on ARAC's recommendations.

Summary of the NPRM

The FAA published a notice of proposed rulemaking (NPRM) on March 26, 2008 (73 FR 15955). The proposal adds a new definition to § 1.1, changes to § 33.7, and introduces § 33.84. These proposed changes would add a new engine overtorque test, amend engine ratings and operating limitations, and define maximum engine overtorque for certain turbopropeller and turboshaft engines. The proposal would harmonize U.S. and European standards for approving engine overtorque transients for turbopropeller and turboshaft engines with free power turbines. The comment period closed June 24, 2008.

Summary of Comments

The FAA received four comment letters, one from a British engine manufacturer (Rolls-Royce Corporation), one from a foreign regulatory authority (Transport Canada), and two from law students at the University of Central Missouri. All four comment letters support the general intent of the proposed rule. However, Transport Canada raised specific concerns that were addressed by clarifying revisions to proposed §§ 33.7 and 33.84. A detailed discussion of changes to the final rule is presented below.

Discussion of the Final Rule

The final rule establishes a standard for applicants to use when applying for and obtaining approval of a maximum engine overtorque limit. This rule harmonizes FAA and EASA standards and simplifies airworthiness approvals for the import and export of turbopropeller and turboshaft engines with free power turbines. The rule also improves safety by stating clear requirements for maximum engine overtorque limits.

Below are specific comments from Transport Canada and our responses to them.

1. The approach proposed, to seek an “approval” for overtorque, is inconsistent with the approach used for “overspeed” and “overtemperature”. Transport Canada suggested the approach for “overtorque” be similar to “overspeed” and “overtemperature”.

We do not agree. Overspeed and overtemperature are transients which are approved when they occur during normal engine operation, e.g., a short duration transient exceedance of a rating (speed, temperature, or torque) as the engine stabilizes at a new operating condition following an acceleration. As proposed in the NPRM, the “maximum engine overtorque” is optional to the applicant. This optional operating condition is not an approved transient, but an “over limit” condition which may occur due to a failure. The applicant can choose whether to declare any maximum engine overtorque. However, to ensure the regulation is clear, we have revised proposed § 33.7 to clarify that engine ratings and operating limitations include both the existing transient engine overtorque and the new maximum engine overtorque “over limit”. We also revised § 33.87(a)(8) to clarify the requirement applies to all transient functions, including engine overtorque. This makes clear that transient engine overtorque is addressed in § 33.87(a)(8) and maximum engine overtorque in § 33.84.

2. The definition of “Maximum engine overtorque” in § 1.1 is not necessary since part 33 does not have similar definitions for “overspeed” or “overtemperature”.

The FAA does not agree. Overspeed and overtemperature in part 33 are transient events and part of the normal operation of the engine as defined in the type design. Maximum engine overtorque is an “over limit” condition that could last up to 20 seconds and is a result of some failure. A definition in § 1.1 is necessary as maximum engine overtorque is unique in its application to turbopropeller and turboshaft engines. Explanation is required to define the context in which this condition would apply and specific exclusions related to it. Transient overspeed and overtemperature are general and well understood terms used widely throughout part 33. No maintenance action is necessary by the aircraft operator provided the cause of the failure is corrected, and the engine meets the new maximum engine overtorque limit requirement.

3. The proposed § 33.84 overtorque test requirement should be independent from the § 33.87 endurance test requirement. Transport Canada also proposed the overtorque test requirement be at least 10% torque over Start Printed Page 45309the highest torque limit for any rating longer than 2 minutes.

We agree, in part, that the overtorque and endurance tests may be performed separately. However, we did not set an overtorque limit because it is the applicant's responsibility to decide the maximum engine overtorque for the engine.

Lastly, we made a clarifying change to wording in the first sentence of § 33.84(b)(4). This change did not alter our intent or the meaning of the proposed regulation.

Paperwork Reduction Act

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

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. The FAA has reviewed the corresponding ICAO Standards and Recommended Practices and determined there are no differences with these regulations.

Regulatory Evaluation Summary

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

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 (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 the private sector, of $100 million or more annually (adjusted for inflation with base year of 1995). This portion of the preamble summarizes the FAA's analysis of the economic impacts of this final rule.

Department of Transportation Order DOT 2100.5 prescribes policies and procedures for simplification, analysis, and review of regulations. If the expected cost impact is so minimal that a proposed or final rule does not warrant a full evaluation, this order permits that a statement to that effect and the basis for it be included in the preamble if a full regulatory evaluation of the cost and benefits is not prepared. Such a determination has been made for this final rule. The reasoning for this determination follows:

This final rule coordinates FAA engine requirements with existing EASA engine requirements that manufacturers must currently meet in order for their engines to be used in European operations. Consequently, this rule will allow engine manufacturers to meet one requirement rather than separate requirements for FAA/EASA certification. There were no public comments on the economic impact of the NPRM. As a result, the expected outcome will be a minimal impact with positive net benefits.

A regulatory evaluation was not prepared. This final rule incorporates existing certification practices, while maintaining the existing level of safety. The benefits of this rule justify the costs and the existing level of safety will be preserved. The Office of Management and Budget has determined that this final rule is a “significant regulatory action” because it harmonizes U.S. aviation standards with those of other civil aviation authorities.

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.

We stated in the initial Regulatory Flexibility Analysis that we believed the rule would be a cost-relieving rule as it harmonizes with the EASA aviation regulations. We received no comments to the contrary.

Therefore, as the FAA Administrator, I certify that this rule will not have a significant economic impact on a substantial number of small entities.

International Trade Analysis

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 any 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 standards have a legitimate domestic objective, such as the protection of safety, and do 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. This rule uses international standards as the basis for regulation and thus is consistent with the Trade Agreements 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 Start Printed Page 45310regulatory action.” The FAA currently uses an inflation-adjusted value of $136.1 million in lieu of $100 million. This final 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 will not have a substantial direct effect on the States, on the relationship between the Federal Government and the States, or on the distribution of power and responsibilities among the various levels of government, and, therefore, does not have federalism implications.

Environmental Analysis

FAA Order 1050.1E identifies FAA actions that are categorically excluded from preparation of an environmental assessment or environmental impact statement under the National Environmental Policy Act in the absence of extraordinary circumstances. The FAA has determined this 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 final rule 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.

Availability of Rulemaking Documents

You can get an electronic copy of rulemaking documents using the Internet by—

1. Searching the Federal eRulemaking Portal (;

2. Visiting the FAA's Regulations and Policies Web page at​regulations_​policies/​; or

3. Accessing the Government Printing Office's Web page at​fr/​index.html.

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 amendment number or docket number of this rulemaking.

Anyone is able to search the electronic form of all comments received into any of our dockets by the name of the individual submitting the comment (or signing the comment, if submitted on behalf of an association, business, labor union, etc.). You may review DOT's complete Privacy Act statement in the Federal Register published on April 11, 2000 (Volume 65, Number 70; Pages 19477-78) or you may visit

Small Business Regulatory Enforcement Fairness Act

The Small Business Regulatory Enforcement Fairness Act (SBREFA) of 1996 requires FAA to comply with small entity requests for information or advice about compliance with statutes and regulations within its jurisdiction. If you are a small entity and you have a question regarding this document, you may contact your local FAA official, or the person listed under the FOR FURTHER INFORMATION CONTACT heading at the beginning of the preamble. You can find out more about SBREFA on the Internet at​regulationspolicies/​rulemaking/​sbre_​act/​.

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List of Subjects

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The Amendment

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In consideration of the foregoing, the Federal Aviation Administration amends parts 1 and 33 of Title 14, Code of Federal Regulations (

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

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Authority: 49 U.S.C. 106(g), 40113, 44701-44702, 44704.

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2. Amend § 1.1 by adding the definition of “Maximum engine overtorque” in alphabetical order, to read as follows:

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General definitions.
* * * * *

Maximum engine overtorque, as it applies to turbopropeller and turboshaft engines incorporating free power turbines for all ratings except one engine inoperative (OEI) ratings of two minutes or less, means the maximum torque of the free power turbine rotor assembly, the inadvertent occurrence of which, for periods of up to 20 seconds, will not require rejection of the engine from service, or any maintenance action other than to correct the cause.

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

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Authority: 49 U.S.C. 106(g), 40113, 44701-44702, 44704.

End Authority Start Amendment Part

4. Amend § 33.7 by redesignating paragraph (c)(16) as (c)(18) and adding new paragraphs (c)(16) and (c)(17) to read as follows:

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Engine ratings and operating limitations.
* * * * *

(c) * * *

(16) Transient engine overtorque, and number of overtorque occurrences.

(17) Maximum engine overtorque for turbopropeller and turboshaft engines incorporating free power turbines.

* * * * *
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5. Section 33.84 is added to read as follows:

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Engine overtorque test.

(a) If approval of a maximum engine overtorque is sought for an engine incorporating a free power turbine, compliance with this section must be demonstrated by testing.

(1) The test may be run as part of the endurance test requirement of § 33.87. Alternatively, tests may be performed on a complete engine or equivalent testing on individual groups of components.

(2) Upon conclusion of tests conducted to show compliance with this section, each engine part or individual groups of components must meet the requirements of § 33.93(a)(1) and (a)(2).

(b) The test conditions must be as follows:

(1) A total of 15 minutes run at the maximum engine overtorque to be approved. This may be done in separate runs, each being of at least 21/2 minutes duration.

(2) A power turbine rotational speed equal to the highest speed at which the maximum overtorque can occur in service. The test speed may not be more than the limit speed of take-off or OEI ratings longer than 2 minutes.

(3) For engines incorporating a reduction gearbox, a gearbox oil temperature equal to the maximum temperature when the maximum engine overtorque could occur in service; and for all other engines, an oil temperature within the normal operating range.Start Printed Page 45311

(4) A turbine entry gas temperature equal to the maximum steady state temperature approved for use during periods longer than 20 seconds when operating at conditions not associated with 30-second or 2 minutes OEI ratings. The requirement to run the test at the maximum approved steady state temperature may be waived by the FAA if the applicant can demonstrate that other testing provides substantiation of the temperature effects when considered in combination with the other parameters identified in paragraphs (b)(1), (b)(2) and (b)(3) of this section.

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6. Amend § 33.87 by revising paragraph (a)(8) to read as follows:

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Endurance test.

(a) * * *

(8) If the number of occurrences of either transient rotor shaft overspeed, transient gas overtemperature or transient engine overtorque is limited, that number of the accelerations required by paragraphs (b) through (g) of this section must be made at the limiting overspeed, overtemperature or overtorque. If the number of occurrences is not limited, half the required accelerations must be made at the limiting overspeed, overtemperature or overtorque.

* * * * *
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Issued in Washington, DC, on August 21, 2009.

J. Randolph Babbitt,


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[FR Doc. E9-20960 Filed 9-1-09; 8:45 am]