[Federal Register Volume 63, Number 94 (Friday, May 15, 1998)]
[Proposed Rules]
[Pages 27001-27002]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-12915]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 98-ANE-18-AD]
RIN 2120-AA64


Airworthiness Directives; General Electric Company CF6-6 Series 
Turbofan 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 Company (GE) CF6-
6 series turbofan engines. This proposal would require removal from 
service of affected low pressure turbine (LPT) stage 4 disks prior to 
reaching new, reduced cyclic life limits, and replacement with 
serviceable parts. This proposal is prompted by reports of LPT stage 4 
disk cracking in the blade dovetail slot bottom area. The actions 
specified by the proposed AD are intended to prevent LPT stage 4 disk 
cracking, which could result in an uncontained engine failure and 
damage to the aircraft.

DATES: Comments must be received by June 15, 1998.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), New England Region, Office of the Regional 
Counsel, Attention: Rules Docket No. 98-ANE-18-AD, 12 New England 
Executive Park, Burlington, MA 01803-5299. Comments may also be sent 
via the Internet using the following address: ``<a href="/cdn-cgi/l/email-protection#10293d71743d1a757e77797e7560627f60507671713e747f643e777f66">9-ad-
<span class="__cf_email__" data-cfemail="2a4f444d43444f5a58455a6a4c4b4b044e455e044d455c">[email protected]</span></a>''. Comments sent via the Internet must contain 
the docket number in the subject line. Comments may be inspected at 
this location between 8:00 a.m. and 4:30 p.m., Monday through Friday, 
except Federal holidays.

FOR FURTHER INFORMATION CONTACT: Karen Curtis, Aerospace Engineer, 
Engine Certification Office, FAA, Engine and Propeller Directorate, 12 
New England Executive Park, Burlington, MA 01803-5299; telephone (781) 
238-7192, fax (781) 238-7199.

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 98-ANE-18-AD.'' 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 Regional Counsel, 
Attention: Rules Docket No. 98-ANE-18-AD, 12 New England Executive 
Park, Burlington, MA 01803-5299.

Discussion

    The Federal Aviation Administration (FAA) has received reports of 
low

[[Page 27002]]

pressure turbine (LPT) stage 4 disk cracking on General Electric 
Company (GE) CF6-6 series turbofan engines. The investigation revealed 
that the dovetail slot bottoms of the LPT stage 4 disks, part numbers 
(P/Ns) 9010M40P01, 9010M40P02, 9010M40P07, 9010M40P09, and 9010M40P12, 
have higher than predicted levels of stress during engine operation. In 
addition, the low cycle fatigue (LCF) material properties have been 
found to be lower than the original design intent. The disk cracks were 
found by inspection during engine shop visits. Extensive material 
testing, and stress and life analyses revealed a minimum calculated LCF 
cyclic life lower than the published LCF cyclic retirement life for the 
stage 4 LPT disks. This condition, if not corrected, could result in 
LPT stage 4 disk cracking, which could result in an uncontained engine 
failure and damage to the aircraft.
    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 removal from service of affected LPT stage 4 
disks prior to reaching new, reduced cyclic life limits, and 
replacement with serviceable parts .
    There are approximately 257 engines of the affected design in the 
worldwide fleet. The FAA estimates that 242 engines installed on 
aircraft of U.S. registry would be affected by this proposed AD, and 
that required parts, on a prorated basis, would cost approximately 
$22,432 per engine. Based on these figures, the total cost impact of 
the proposed AD on U.S. operators is estimated to be $5,428,544.
    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 U.S.C. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

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

General Electric Company: Docket No. 98-ANE-18-AD.

    Applicability: General Electric Company (GE) CF6-6 series 
turbofan engines, installed on but not limited to McDonnell Douglas 
DC-10-10 series aircraft.

    Note 1: 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 (d) 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 low pressure turbine (LPT) stage 4 disk cracking, 
which could result in an uncontained engine failure and damage to 
the aircraft, accomplish the following:
    (a) Remove from service LPT stage 4 disks, part numbers (P/Ns) 
9010M40P01, 9010M40P02, 9010M40P07, 9010M40P09, and 9010M40P12, and 
replace with serviceable parts, in accordance with the following 
schedule:
    (1) For disks with 12,300 or more cycles since new (CSN) but 
less than 24,000 CSN on the effective date of this AD, remove from 
service affected disks at the earliest of the following:
    (i) The next piece-part exposure after the effective date of 
this AD; or
    (ii) The next engine shop visit after accumulating 16,500 CSN; 
or
    (iii) Within 4,200 cycles in service (CIS) after the effective 
date of this AD; or
    (iv) Prior to exceeding 24,000 CSN.
    (2) For disks with 5,000 or more CSN, but less than 12,300 CSN, 
on the effective date of this AD, remove from service affected disks 
at the earlier of the following:
    (i) Prior to exceeding 16,500 CSN; or
    (ii) Within 7,300 CIS after the effective date of this AD.
    (3) For disks with less than 5,000 CSN on the effective date of 
this, remove from service affected disks prior to exceeding 12,300 
CSN.
    (b) This AD establishes a new cyclic retirement life limit for 
LPT stage 4 disks of 12,300 CSN. Thereafter, except as provided in 
paragraph (d) of this AD, no alternative cyclic retirement life 
limits may be approved for LPT stage 4 disks.
    (c) For the purpose of this AD, the following definitions apply:
    (1) An engine shop visit is defined as separation of a major, 
static flange.
    (2) Piece-part exposure is when the affected part is completely 
disassembled in accordance with the disassembly instructions in the 
engine manual or section of the Instructions for Continued 
Airworthiness (ICA).
    (d) 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. 
Operators shall submit their requests through an appropriate FAA 
Principal Maintenance Inspector, who may add comments and then send 
it to the Manager, Engine Certification Office.

    Note 2: Information concerning the existence of approved 
alternative methods of compliance with this airworthiness directive, 
if any, may be obtained from the Engine Certification Office.

    (e) 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 May 7, 1998.
Thomas A. Boudreau,
Acting Manager, Engine and Propeller Directorate, Aircraft 
Certification Service.
[FR Doc. 98-12915 Filed 5-14-98; 8:45 am]
BILLING CODE 4910-13-U


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