Airworthiness Directives; General Electric Company CF6-6 Series Turbofan Engines

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: ``9-ad-

[email protected]''. 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

e 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

card 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

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

e 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]

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:

safe 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.