28430 Federal Register / Vol. 61, No. 108 / Tuesday, June 4, 1996 / Rules and Regulations

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.

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

§ 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 § 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
Federal Register / Vol. 61, No. 108 / Tuesday, June 4, 1996 / Rules and Regulations 28431

to § 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
28432 Federal Register / Vol. 61, No. 108 / Tuesday, June 4, 1996 / Rules and Regulations

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 § 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 § 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 § 33.74 and the

amendments to § 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.
Federal Register / Vol. 61, No. 108 / Tuesday, June 4, 1996 / Rules and Regulations 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:

§ 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:

§ 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

§ 33.75 (a) through (c).

4. Section 33.83 is revised to read as

follows:

§ 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

§ 33.5.

5. Section 33.92 is revised to read as

follows:

§ 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]

BILLING CODE 4910–13–M