AD 2000-25-06

This amendment adopts a new airworthiness directive (AD) that is applicable to certain Pratt & Whitney (PW) PW4000 turbofan engines with the current design low pressure turbine (LPT) 4th stage air seal installed. This action requires, based on engine model, replacement of the current design seal with a new design seal, or with a modified seal. This amendment is prompted by reports of cracks in LPT 4th stage air seals. The actions specified by this AD are intended to reduce stresses that could lead to LPT 4th stage air seal cracking, resulting in seal fracture, uncontained engine failure, and damage to the airplane.

Final rule, request for comments

2000-25-06 Pratt & Whitney: Amendment 39-12040. Docket 2000-NE-43-AD.

Applicability:
This airworthiness directive is applicable to Pratt & Whitney (PW) PW4052, PW4056, PW4060, PW4060A, PW4062, PW4152, PW4156, PW4156A, PW4158, PW4164, PW4168, PW4168A, PW4460, and PW4462 turbofan engines, with low pressure turbine (LPT) 4th stage air seal, part number (P/N) 50N478 or P/N 50N478-001 installed. These engines are installed on but not limited to Boeing 747, 767, McDonnell Douglas MD-11, Airbus Industrie A300, A310, and A330 series airplanes.

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:
Compliance with this AD is required as indicated, unless already done.

To reduce stresses that could lead to fatigue cracking of the LPT 4th stage air seal, resulting in seal fracture, uncontained engine failure, and damage to the airplane, do the following:

(a) If the limits in Table 1 of this AD for 4th stage air seal P/N 50N478 or P/N 50N478-001 have been exceeded, replace with a serviceable part prior to further flight.

(b) Replace 4th stage air seal, P/N 50N478 or 50N478-001, with a serviceable part, based on engine model, prior to exceeding the cycles-since-new (CSN) or cycles-in-service (CIS) time limits in Table 1 of this AD.

Table1. 4th Stage Air Seal Time Limits.

Engine Model
4th Stage Air Seal P/N
Cycles-since-new (CSN) on Effective Date of This AD
Limit
(1) PW4052, PW4060, PW4060A, PW4156, and PW4158.
50N478.
Fewer than or equal to 8,000 CSN.
8,000 CSN
(2) PW4056, PW4152, PW4156A, and PW4460, that have incorporated service bulletin (SB) PW4ENG 72-657, Revision 1, dated July 19, 2000.
50N478.
Fewer than or equal to 8,000 CSN.
8,000 CSN
(3) PW4056, PW4152, PW4156A, and PW4460, that have not incorporated SB PW4ENG 72-657, Revision 1, dated July 19, 2000.
50N478.
Fewer than or equal to 4,500 CSN.
4,500 CSN
(4) PW4062 and PW4462.
50N478.
Fewer than or equal to 7,000 CSN.
7,000 CSN
(5) PW4164, PW4168, and PW4168A.
(i) 50N478 or 50N478-001
Fewer than or equal to 3,000 CSN.
4,500 CSN

(ii) 50N478 or 50N478-001
More than 3,000 CSN but fewer than or equal to 4,500 CSN
1,500 CIS after the effective date of this AD

(iii) 50N478 or 50N478-001
More than 4,500 CSN but fewer than 6,000 CSN
6,000 CSN

(c) For the purposes of this AD, a serviceable part is defined in Table 2 as follows:

Table 2. Serviceable Parts.

For Engine Models
Serviceable P/N
(1) PW4052, PW4056, PW4060, PW4060A, PW4062, PW4152, PW4156, PW4156A, PW4158, PW4460, and PW4462.
51N038 or 50N478-001.
(2) PW4164, PW4168, and PW4168A.
51N038.

Alternative Methods of Compliance
(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.

Special Flight Permits
(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 inspection and rework requirements of this AD can be accomplished.

Effective Date of This AD
(f) This amendment becomes effective December 29, 2000.

The FAA recently received reports of five LPT 4th stage air seals found cracked. An investigation revealed that the cracking is being caused by excessive axial loads on the air seal. The thermal environment and mechanical loads are causing the current design LPT 4th stage air seals to grow radially and axially. This is causing insufficient distance between the LPT stage 3 disk and LPT stage 4 disk, that results in an excessive axial load leading to air seal cracks. This action requires, based on engine model, replacement of the current design seal with a new design seal, or with a modified seal. This amendment is prompted by reports of cracks in LPT 4th stage air seals. The actions specified by this AD are intended to reduce stresses that could lead to LPT 4th stage air seal cracking, resulting in seal fracture, uncontained engine failure, and damage to the airplane. Pratt & Whitney has issued two relevant Alert Service Bulletins, (ASB) No. PW4G- 100-A72-155, Revision 1, dated October 27, 2000, and ASB No. PW4ENG A72-707, Revision 1, dated October 27, 2000. The ASB's introduce a new design LPT 4th stage air seal P/N 51N038, and provide instructions for modifying the current design air seal P/N 50N478 to increase service life.

Required Actions
Since the unsafe condition described is likely to exist or develop on other engines of the same type design that are certificated for operation in the United States, this AD is being issued to replace, based on engine model, the current design seal P/N 50N478 with a new design seal P/N 51N038, or modification of the current design seal. This AD is also being issued to reduce stresses that could lead to LPT 4th stage air seal cracking, resulting in seal fracture, uncontained engine failure, and damage to the airplane.

Immediate Adoption
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. 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.

Commentsare 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 2000-NE-43-AD." The postcard will be date stamped and returned to the commenter.

Regulatory Impact
The regulations adopted herein will not have a substantial direct effect 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, it is determined that this final rule does not have federalism implications under Executive Order (EO) No. 13132.

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 EO No. 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, Safety.

Adoption of the Amendment
Accordingly, pursuantto the authority delegated to me by the Administrator, the Federal Aviation Administration amends 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.

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