[Federal Register Volume 59, Number 13 (Thursday, January 20, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-1103]


[[Page Unknown]]

[Federal Register: January 20, 1994]


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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: 

------------------------------------------------------------------------
            Document No.              Pages     Revision        Date    
------------------------------------------------------------------------
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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