[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: ``engineprop@faa.dot.gov''. 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
