Airworthiness Directives; Textron Lycoming Model T5508D Turboshaft Engines

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 93-ANE-56; Amendment 39-8798; AD 94-02-01]

Airworthiness Directives; Textron Lycoming Model T5508D

Turboshaft Engines

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule, request for comments.

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SUMMARY: This amendment adopts a new airworthiness directive (AD) that

is applicable to Textron Lycoming Model T5508D turboshaft engines. This

action requires a cyclic life reduction for the T5508D impeller, a more

conservative method for determining low cycle fatigue (LCF) damage to

the impeller, and a method for prorating past impeller usage, based on

the new LCF counting factors. This amendment is prompted by a report of

a rotorcraft accident found to have been caused by an uncontained

impeller failure. A subsequent field campaign inspection of high-time

impellers utilized by heavy lift operators confirmed 12 more impellers

with similar distress. The actions specified in this AD are intended to

prevent an impeller failure, which can result in an uncontained engine

failure, inflight shutdown, or possible rotorcraft damage.

DATES: Effective February 4, 1994.

The incorporation by reference of certain publications listed in

the regulations is approved by the Director of the Federal Register as

of February 4, 1994.

Comments for inclusion in the Rules Docket must be received on or

before March 21, 1994.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

Administration (FAA), Office of the Assistant Chief Counsel, Attention:

Rules Docket No. 93-ANE-56, 12 New England Executive Park, Burlington,

MA 01803-5299.

The service information referenced in this AD may be obtained from

Textron Lycoming, 550 Main Street, Stratford, CT 06497. This

information may be examined at the FAA, New England Region, Office of

the Assistant Chief Counsel, Attn: Rules Docket No. 93-ANE-56, 12 New

England Executive Park, Burlington, Massachusetts; or at the Office of

the Federal Register, 800 North Capitol Street, NW., suite 700,

Washington, DC.

FOR FURTHER INFORMATION CONTACT: Daniel Kerman, Aerospace Engineer,

Engine Certification Office, FAA, Engine and Propeller Directorate, 12

New England Executive Park, Burlington, MA 01803-5299; telephone (617)

238-7130, fax (617) 238-7199.

SUPPLEMENTARY INFORMATION: The Federal Aviation Administration (FAA)

received a report of a rotorcraft accident caused by an uncontained

failure of a Textron Lycoming T5508D compressor impeller. The impeller

failure was caused by a low cycle fatigue (LCF) crack which initiated

and propagated to failure in the impeller aft face cooling air holes.

Based on this accident, Textron Lycoming issued a Service Bulletin (SB)

requiring all operators to inspect impellers with greater than 5,000

cycles in service (CIS). To date, 12 impellers have been discovered

with distress in the impeller aft face cooling air holes similar to the

accident aircraft but of lesser magnitude. Subsequent analysis and

testing of this current design impeller, as well as service experience,

has revealed a lower LCF life than originally calculated. This lower

LCF life is based on a new engineering analysis using different,

improved component geometry and LCF material properties than were used

in the original engineering lifing analysis for the impeller. In

addition to arriving at a lower LCF life, the new engineering analysis

also derived the updated impeller cyclic counting factors.

Configuration-specific material testing, combined with updated operator

mission profiles, revealed a need to update the impeller cyclic

counting factors because minor cyclic LCF damage was greater than

previously calculated. This condition, if not corrected, can result in

impeller failure, which can result in an uncontained engine failure,

inflight shutdown, or possible rotorcraft damage.

This amendment requires a cyclic life reduction for the impeller, a

more conservative sub-cycle counting factors table, and a method for

prorating past impeller usage based on the new cyclic counting factors.

For those impellers that exceed the new life limit, a drawdown schedule

will be implemented for safe removal of time-expired impellers. This

program is substantiated by the demonstrated correlation between spin

pit testing of actual cracked parts, engineering analysis,

configuration specimen fatigue testing, and field service experience. A

safety assessment has also been performed to substantiate the drawdown

schedule for time-expired impellers to conservatively manage these

impellers beyond the new life limits.

The FAA has reviewed and approved the technical contents of Textron

Lycoming SB No. T5508D-0040, dated June 25, 1993, that describes the

removal schedule necessary for those impellers that exceed the new life

limits, and Textron Lycoming SB No. T5508D-0002, Revision 7, dated June

25, 1993, that reduces the cyclic life limit of the impeller from

16,600 to 8,000 cycles, revises the minor cycle counting factors table

used for cyclic computation, and provides a method for prorating past

impeller usage based on the new cycle counting factors.

Since an unsafe condition has been identified that is likely to

exist or develop on other products of this same type design, this AD is

being issued to prevent impeller failure, which can result in an

uncontained engine failure, inflight shutdown, or possible rotorcraft

damage. This AD requires a cyclic life reduction for the impeller, a

more conservative sub-cycle counting factors table, and a method for

prorating past impeller usage based on the new cycle counting factors.

For those impellers that exceed the new life limit, the FAA has

established a drawdown schedule for safe removal. These actions are

required to be accomplished in accordance with the service bulletins

described previously.

Since a situation exists that requires the immediate adoption of

this regulation, it is found that notice and opportunity for prior

public comment hereon are impracticable, and that good cause exists for

making this amendment effective in less than 30 days.

Comments Invited

Although this action is in the form of a final rule that involves

requirements affecting flight safety and, thus, was not preceded by

notice and an opportunity for public comment, comments are invited on

this rule. Interested persons are invited to comment on this rule by

submitting such written data, views, or arguments as they may desire.

Communications should identify the Rules Docket number and be submitted

in triplicate to the address specified under the caption ADDRESSES. All

communications received on or before the closing date for comments will

be considered, and this rule may be amended in light of the comments

received. Factual information that supports the commenter's ideas and

suggestions is extremely helpful in evaluating the effectiveness of the

AD action and determining whether additional rulemaking action would be

needed.

Comments are specifically invited on the overall regulatory,

economic, environmental, and energy aspects of the rule that might

suggest a need to modify the rule. All comments submitted will be

available, both before and after the closing date for comments, in the

Rules Docket for examination by interested persons. A report that

summarizes each FAA-public contact concerned with the substance of this

AD will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments

submitted in response to this notice must submit a self-addressed,

stamped postcard on which the following statement is made: ``Comments

to Docket Number 93-ANE-56.'' The postcard will be date stamped and

returned to the commenter.

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 final

rule does not have sufficient federalism implications to warrant the

preparation of a Federalism Assessment.

The FAA has determined that this regulation is an emergency

regulation that must be issued immediately to correct an unsafe

condition in aircraft, and is not a ``significant regulatory action''

under Executive Order 12866. It has been determined further that this

action involves an emergency regulation under DOT Regulatory Policies

and Procedures (44 FR 11034, February 26, 1979). If it is determined

that this emergency regulation otherwise would be significant under DOT

Regulatory Policies and Procedures, a final regulatory evaluation will

be prepared and placed in the Rules Docket. A copy of it, if filed, may

be obtained from the Rules Docket at the location provided under the

caption ADDRESSES.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Incorporation by

reference, Safety.

Adoption of the Amendment

Accordingly, pursuant to the authority delegated to me by the

Administrator, the Federal Aviation Administration amends 14 CFR part

39 of the Federal Aviation Regulations as follows:

PART 39--AIRWORTHINESS DIRECTIVES

1. The authority citation for part 39 continues to read as follows:

Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C.

106(g); and 14 CFR 11.89.

Sec. 39.13 [Amended]

2. Section 39.13 is amended by adding the following new

airworthiness directive:

94-02-01 Textron Lycoming: Amendment 39-8798. Docket 93-ANE-56.

Applicability: Textron Lycoming Model T5508D turboshaft engines,

installed on but not limited to Bell 214B helicopters.

Compliance: Required as indicated, unless accomplished

previously.

To prevent an impeller failure, which can result in an

uncontained engine failure, inflight shutdown, or possible

rotorcraft damage, accomplish the following:

(a) Within 7 days after the effective date of this AD, conduct a

revised impeller operating cycle count (prorate), in accordance with

paragraph E of Textron Lycoming Service Bulletin (SB) No. T5508D-

0002, Revision 7, dated June 25, 1993.

(b) Following the implementation of the revised cycle count

methodology, specified in paragraph (a) of this AD, replace those

impellers installed in aircraft that exceed the new life limit, on

the effective date of this AD, in accordance with the drawdown

requirements defined in Table 1 of Textron Lycoming SB T5508D-0040,

dated June 25, 1993.

(c) For those impellers not installed in aircraft on the

effective date of this AD, with 8,000 or more cycles in service

(CIS), replace with a new or serviceable impeller prior to further

flight.

(d) Thereafter, Textron Lycoming Model T5508D impeller, part

numbers 2-100-180-13 and 2-100-180-19, are life limited to 8,000

CIS, as defined in Table 1 of Textron Lycoming SB No. T5508D-0002,

Revision 7, dated June 25, 1993.

(e) An alternative method of compliance or adjustment of the

compliance time that provides an acceptable level of safety may be

used if approved by the Engine Certification Office. The request

should be forwarded through an appropriate FAA Principal Maintenance

Inspector, who may add comments and then send it to the Engine

Certification Office.

Note: Information concerning the existence of approved

alternative methods of compliance with this airworthiness directive,

if any, may be obtained from the Engine Certification Office.

(f) The operational cyclic counting and replacement of impellers

shall be done in accordance with the following service bulletins:

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Document No. Pages Revision Date

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Textron Lycoming, SB No. T5508D-0002 1-12 7........... June 25,

1993.

Total pages: 12

Textron Lycoming, SB No. T5508D-0040 1-2 Original.... June 25,

1993.

Total pages: 2

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This incorporation by reference was approved by the Director of the

Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part

51. Copies may be obtained from Textron Lycoming, 550 Main Street,

Stratford, CT 06497. Copies may be inspected at the FAA, Office of

the Assistant Chief Counsel, Attention: Rules Docket No. 93-ANE-56,

12 New England Executive Park, Burlington, Massachusetts; or at the

Office of the Federal Register, 800 North Capitol Street, NW., suite

700, Washington, DC.

(g) This amendment becomes effective on February 4, 1994.

Issued in Burlington, Massachusetts, on January 10, 1994.

Jay J. Pardee,

Acting Manager, Engine and Propeller Directorate, Aircraft

Certification Service.

[FR Doc. 94-1103 Filed 1-19-94; 8:45 am]

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