96-23755. Airworthiness Directives; General Electric Aircraft Engines CT7 Series Turboprop Engines

[Federal Register Volume 61, Number 181 (Tuesday, September 17, 1996)]
[Proposed Rules]
[Pages 48866-48867]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-23755]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 96-ANE-06]
RIN 2120-AA64


Airworthiness Directives; General Electric Aircraft Engines CT7 
Series Turboprop Engines

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to General Electric Aircraft Engines 
(GE) CT7 series turboprop engines. This proposal would require 
replacement of the gas generator turbine stage 2 forward cooling plates 
prior to the published cyclic life limits. The proposal also defines 
the new, reduced cyclic life limits for the affected forward cooling 
plates. This proposal is prompted by reports of gas generator turbine 
stage 2 forward cooling plate failures. The actions specified by the 
proposed AD are intended to prevent gas generator turbine stage 2 
forward cooling plate failure, which could result in an uncontained 
engine failure.

DATES: Comments must be received by October 17, 1996.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), New England Region, Office of the Assistant Chief 
Counsel, Attention: Rules Docket No. 96-ANE-06, 12 New England 
Executive Park, Burlington, MA 01803-5299. Comments may be inspected at 
this location between 8:00 a.m. and 4:30 p.m., Monday through Friday, 
except Federal holidays.
    The service information referenced in the proposed rule may be 
obtained from GE Aircraft Engines, 1000 Western Ave., Lynn, MA 01910; 
telephone [phone], fax [phone]. This information may be 
examined at the FAA, New England Region, Office of the Assistant Chief 
Counsel, 12 New England Executive Park, Burlington, MA.

FOR FURTHER INFORMATION CONTACT: Dave Keenan, Aerospace Engineer, 
Engine Certification Office, FAA, Engine and Propeller Directorate, 12 
New England Executive Park, Burlington, MA 01803-5299; telephone (617) 
238-7139, fax [phone].

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to participate in the making of the 
proposed 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 above. All 
communications received on or before the closing date for comments, 
specified above, will be considered before taking action on the 
proposed rule. The proposals contained in this notice may be changed in 
light of the comments received.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed 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 summarizing each FAA-public contact concerned with 
the substance of this proposal 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 96-ANE-06.'' The postcard will be date stamped and 
returned to the commenter.

Availability of NPRMs

    Any person may obtain a copy of this NPRM by submitting a request 
to the FAA, New England Region, Office of the Assistant Chief Counsel, 
Attention: Rules Docket No. 96-ANE-06, 12 New England Executive Park, 
Burlington, MA 01803-5299.

Discussion

    The Federal Aviation Administration (FAA) has received reports of 
gas generator turbine stage 2 forward cooling plate failures on General 
Electric Aircraft Engines (GE) CT7 series turboprop engines. In one 
incident the gas generator turbine stage 2 forward

[[Page 48867]]

cooling plate failure caused an engine uncontainment. The investigation 
revealed that the failures were caused by low cycle fatigue (LCF) of 
the gas generator turbine stage 2 forward cooling plate. In addition, 
the investigation revealed that the cooling plates can be exposed to 
higher temperatures if certain combinations of clearances, leakage, 
ambient conditions, and/or engine conditions exist, in which case the 
cooling plates can be subjected to the combined effects of creep and 
LCF. This condition, if not corrected, could result in gas generator 
turbine stage 2 forward cooling plate failure, which could result in an 
uncontained engine failure.
    The FAA has reviewed and approved the technical contents of GE 
Aircraft Engines (CT7-TP Series) Service Bulletin (SB) A72-381, dated 
January 17, 1996, that describes procedures for replacement of affected 
gas generator turbine stage 2 forward cooling plates and defines new, 
reduced cyclic life limits.
    Since an unsafe condition has been identified that is likely to 
exist or develop on other products of this same type design, the 
proposed AD would require replacement of the gas generator turbine 
stage 2 forward cooling plate within 30 days after the effective date 
of this AD, or prior to reaching the new, reduced cyclic life limits 
listed in the Accomplishment Instructions of GE Aircraft Engines (CT7-
TP Series) SB A72-381, dated January 17, 1996, whichever occurs later. 
This compliance end-date was determined based on risk analysis 
methodology. The actions would be required to be accomplished in 
accordance with the SB described previously.
    There are approximately 1,100 engines of the affected design in the 
worldwide fleet. The FAA estimates that 500 engines installed on 
aircraft of U.S. registry would be affected by this proposed AD, that 
it would take approximately 8 work hours per engine to accomplish the 
proposed actions, and that the average labor rate is $60 per work hour. 
Parts will be supplied by the manufacturer to operators under GE's 
Engine Care Maintenance Plan (ECMP). At this time, all operators fall 
under the ECMP. Based on these figures, the total cost impact of the 
proposed AD on U.S. operators is estimated to be $240,000.
    The regulations proposed herein would 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 
proposal would not have sufficient federalism implications to warrant 
the preparation of a Federalism Assessment.
    For the reasons discussed above, I certify that this proposed 
regulation (1) is not a ``significant regulatory action'' under 
Executive Order 12866; (2) is not a ``significant rule'' under the DOT 
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); 
and (3) if promulgated, will not have a significant economic impact, 
positive or negative, on a substantial number of small entities under 
the criteria of the Regulatory Flexibility Act. A copy of the draft 
regulatory evaluation prepared for this action is contained in the 
Rules Docket. A copy of it may be obtained by contacting the Rules 
Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration proposes to amend 
part 39 of the Federal Aviation Regulations (14 CFR part 39) as 
follows:

PART 39--AIRWORTHINESS DIRECTIVES

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

    Authority: 49 USC 106(g), 40113, 44701.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding the following new 
airworthiness directive:

General Electric Aircraft Engines: Docket No. 96-ANE-06.

    Applicability: General Electric Aircraft Engines (GE) Models 
CT7-5A2, -7A, -9B, and -9C turboprop engines, with gas generator 
turbine (GGT) stage 2 forward cooling plates, Part Number (P/N) 
6064T10P01 and P/N 6086T91P02, installed. These engines are 
installed on but not limited to Construcciones Aeronauticas, SA 
(CASA) CN-235 series and SAAB-SCANIA SF340 series aircraft.
    Note: This airworthiness directive (AD) applies to each engine 
identified in the preceding applicability provision, regardless of 
whether it has been modified, altered, or repaired in the area 
subject to the requirements of this AD. For engines that have been 
modified, altered, or repaired so that the performance of the 
requirements of this AD is affected, the owner/operator must request 
approval for an alternative method of compliance in accordance with 
paragraph (c) of this AD. The request should include an assessment 
of the effect of the modification, alteration, or repair on the 
unsafe condition addressed by this AD; and, if the unsafe condition 
has not been eliminated, the request should include specific 
proposed actions to address it.

    Compliance: Required as indicated, unless accomplished 
previously.
    To prevent GGT stage 2 forward cooling plate failure, which 
could result in an uncontained engine failure, accomplish the 
following:
    (a) Within 30 days after the effective date of this AD, or prior 
to reaching the new, reduced cyclic life limits listed in the 
Accomplishment Instructions of GE Aircraft Engines (CT7-TP Series) 
Service Bulletin (SB) A72-381, dated January 17, 1996, whichever 
occurs later, remove from service GGT stage 2 forward cooling 
plates, and replace with a serviceable part, which is defined as a 
GGT stage 2 forward cooling plate that has less than the new, 
reduced cyclic limits on the effective date of this AD, as defined 
in that SB.
    (b) This action establishes the following new, reduced cyclic 
life limits for affected GGT stage 2 forward cooling plates:
    (1) 8,000 cycles since new (CSN) for GGT stage 2 forward cooling 
plates, P/N 6064T10P01, identified by serial numbers listed in 
Tables 1 and 2 of GE Aircraft Engines (CT7-TP Series) SB No. A72-
381, dated January 17, 1996, for GE CT7-5A2, -7A, -9B, and -9C 
engine models.
    (2) 12,000 CSN for GGT stage 2 forward cooling plates, P/N 
6064T10P01 (not listed in (1) above), and P/N 5086T91P02, for GE 
CT7-5A2 and -7A engine models.
    (3) 9,000 CSN for GGT stage 2 forward cooling plates, P/N 
6064T10P01 (not listed in (1) above), and P/N 5086T91P02, for GE 
CT7-9B/-9C engine models.
    (c) 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 Manager, 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 
Manager, 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.
    (d) Special flight permits may be issued in accordance with 
sections 21.197 and 21.199 of the Federal Aviation Regulations (14 
CFR 21.197 and 21.199) to operate the aircraft to a location where 
the requirements of this AD can be accomplished.

    Issued in Burlington, Massachusetts, on September 10, 1996.
Jay J. Pardee,
Manager, Engine and Propeller Directorate, Aircraft Certification 
Service.
[FR Doc. 96-23755 Filed 9-16-96; 8:45 am]
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