AD 96-25-10

This amendment adopts a new airworthiness directive (AD), applicable to Pratt & Whitney JT9D series turbofan engines, that requires installing an improved design turbine exhaust case (TEC) with a thicker containment wall, modifying the existing TEC to incorporate a containment shield, or modifying the existing TEC to replace the "P" flange and case wall. This amendment is prompted by reports of 64 uncontained engine failures since 1972. The actions specified by this AD are intended to prevent release of uncontained debris from the TEC following an internal engine failure, which can result in damage to the aircraft.

Final rule.

96-25-10 Pratt & Whitney: Amendment 39-9853. Docket 95-ANE-57.
Applicability: Pratt & Whitney (PW) JT9D-3, -7, -20, -59A, -70A, -7Q, and -7R4 series turbofan engines, installed on but not limited to Airbus A300 and A310 series; Boeing 747 and 767 series; and McDonnell Douglas DC-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 (b) 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 release of uncontained debris from the turbine exhaust case (TEC) following an internal engine failure, which can result in damage to the aircraft, accomplish the following:
(a) At the next removal of the TEC from the low pressure turbine case "P" flange for overhaul, where the No. 4 bearing, carbon seals, lubrication pressurization lines, or scavenge lines are removed for maintenance after the effective date of this AD, but not later than 48 months after the effective date of this AD, accomplish the following:
(1) For PW JT9D-3A, -7, -7A, -7AH, -7H, -7F, -7J, -20, and -20J series turbofan engines, accomplish any one of the following actions:
(i) Install a thicker-walled TEC, with Part Numbers (P/N's) listed in PW SB No. 6113, dated April 13, 1993, as applicable; or
(ii) Install a modified TEC that incorporates a containment shield, with P/N's listed in PW SB No. 5907, dated March 27, 1990, as applicable; or
(iii) Install a modified TEC that incorporates a replacement "P" flange and case wall, with P/N's listed in PW SB No. 6118, Revision 3, dated January 10, 1996, or
(iv) Install a modified TEC that incorporates a replacement "P" flange and case wall, with Chromalloy Supplemental Type Certificate (STC) SE00047AT-D, dated October 15, 1996.
(2) For PW JT9D-7Q and -7Q3 series turbofan engines, accomplish any one of the following actions:
(i) Install a thicker-walled TEC, with P/N's listed in PW SB No. 5977, dated December 14, 1990; or
(ii) Install a modified TEC that incorporates a containment shield, with P/N's listed in PW SB No. 5907, dated March 27, 1990, as applicable; or
(iii) Install a modified TEC that incorporates a replacement "P" flange and case wall, with P/N's listed in PW SB No. 6157, Revision 1, dated July 17, 1996; or
(iv) Install a modified TEC that incorporates a replacement "P" flange and case wall, with Chromalloy STC SE00047AT-D, dated October 15, 1996.
(3) For PW JT9D-59A and -70A series turbofan engines, accomplish one of the following actions:
(i) Install a thicker-walled TEC, with P/N's listed in PW SB No. 6243, dated February 1, 1996; or
(ii) Install a modified TEC that incorporates a containment shield, with P/N's listed in PW SB No. 5907, dated March 27, 1990, as applicable;
(iii) Install a modified TEC that incorporates a replacement "P" flange and case wall, with P/N's listed in PW SB No. 6157, Revision 1, dated July 17, 1996; or
(iv) Install a modified TEC that incorporates a replacement "P" flange and case wall, with Chromalloy STC SE00047AT-D, dated October 15, 1996.
(4) For PW JT9D-7R4D (BG-700 series) turbofan engines, accomplish one of the following actions:
(i) Install a thicker-walled TEC, with P/N's listed in PW SB No. JT9D-7R4-72- 479, Revision 1, dated November 12, 1993; or(ii) Install a modified TEC that incorporates a containment shield, with P/N's listed in PW SB No. JT9D-7R4-72-407, Revision 1, dated August 16, 1990, as applicable; or
(iii) Install a modified TEC that incorporates a replacement "P" flange and case wall, with Chromalloy STC SE00047AT-D, dated October 15, 1996.
(5) For PW JT9D-7R4D (BG-800 series), -7R4D (BG-900 series), -7R4D1 (AI-500 series), -7R4E (BG-800 series), -7R4E (BG-900 series), -7R4E1 (AI-500 series), -7R4E1 (AI-600 series), -7R4E4 (BG-900 series), -7R4G2 (BG-300 series), and -7R4H1 (AI-600 series) turbofan engines, accomplish any one of the following actions:
(i) Install a thicker-walled TEC, with P/N's listed in PW SB No. JT9D-7R4-72- 534, dated October 18, 1996; or
(ii) Install a modified TEC that incorporates a containment shield, with P/N's listed in PW SB No. JT9D-7R4-72-466, Revision 2, dated May 10, 1996; or
(iii) Install a modified TEC that incorporates a replacement "P" flange and case wall, with P/N's listed in PW SB No. JT9D-7R4-72-534, dated October 18, 1996; or
(iv) Install a modified TEC that incorporates a replacement "P" flange and case wall, with Chromalloy STC SE00054AT-D, dated October 19, 1994.
(6) For PW JT9D-7R4D (BG-800 series), -7R4D (BG-900 series), -7R4D1 (AI-500 series), -7R4E (BG-800 series), -7R4E (BG-900 series), -7R4E1 (AI-500 series), -7R4E1 (AI-600 series), -7R4E4 (BG-900 series), -7R4G2 (BG-300 series), and -7R4H1 (AI-600 series) turbofan engines, with TECs that have been modified to incorporate a replacement "P" flange and case wall, in accordance with PW SB No. JT9D-7R4-72-513, Revision 3, dated November 13, 1996, or previous revisions, perform heat treatment of the TECs in accordance with the Accomplishment Instructions of PW SB No. JT9D-7R4-72-534, dated October 18, 1996.
(b) 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 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.
(c) 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.
(d) The actions required by this AD shall be done in accordance with the following PW SBs:

SB No. 5977
1-6
Original
December 14, 1990
Total pages: 6.

SB No. JT9D-7R4- 72-479
1
1
November 12, 1993

2,3
Original
February 25, 1993

4-6
1
November 12, 1993
Total pages: 6.

SB No. 6243
1-6
Original
February 1, 1996
Total pages: 6.

SB No. JT9D-7R4- 72-513
1-19
3
November 13, 1996
Total pages: 19.

SB No. JT9D-7R4- 72-534
1-26
Original
October 18, 1996
Total pages: 26.

SB No. 5907
1-32
Original
March 27, 1990
Total pages: 32.

SB No. JT9D-7R4- 72-407
1
1
August 16, 1990

2-5
Original
March 30, 1990

6
1
August 16, 1990

7-22
Original
March 30, 1990
Total pages: 22.

SB No. JT9D-7R4- 72-466
1,2
2
May 10, 1996

3-8
Original
January 15, 1993

9-11
1
March 4, 1994

12,13
Original
January 15, 1993

14-16
1
March 4, 1994

17,18
Original
January 15, 1993
Total pages: 18.

SB No. 6118
1
3
January 10, 1996

2-5
2
April 18, 1995

6-32
Original
April 15, 1993

33
2
April 18, 1995

34-38
Original
April 15, 1993

39
1
May 20, 1993

40
Original
April 15, 1993

41-44
1
May 20, 1993

45
3
January 10, 1996
Total pages: 45.

SB No. 6157
1
1
July 17, 1996

2-15
Original
February 9, 1994

16
1
July 17, 1996
Total pages: 16.

This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from Pratt & Whitney, Publications Department, Supervisor Technical Publications Distribution, M/S 132-30, 400 Main St., East Hartford, CT 06108; telephone (860) 565-7700, fax (860) 565-4503. Copies may be inspected at the FAA, New England Region, Office of the Assistant Chief Counsel, 12 New England Executive Park, Burlington, MA; or at the Office of the Federal Register, 800 North Capitol Street NW., suite 700, Washington, DC.
(e) This amendment becomes effective on February 18, 1997.

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to Pratt & Whitney (PW) JT9D series turbofan engines was published in the Federal Register on June 5, 1996 (61 FR 28520). That action proposed to require installing an improved design turbine exhaust case (TEC) with a thicker containment wall, modifying the existing TEC to incorporate a containment shield, or modifying the existing TEC to replace the "P" flange and case wall.
Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.
One commenter states that the proposed modification of the TEC as a solution to preventing uncontained engine failure is unnecessary since there are modifications and inspection programs available that specifically address the root causes for those events that led to uncontained engine failures. The commenter points out that of the 64 incidents of TEC penetration, all but one event are addressed by other mandated actions. The FAA does not concur. Since January 1993, when the FAA first considered issuance of an AD for TEC containment, three additional conditions have occurred that the FAA considers warranting AD action at this time. First, there have been new root cause problems resulting in TEC penetrations; second the rate of uncontained engine failures has increased; and third, more substantial damage to the engine and aircraft has occurred. The discovery of new root causes of failures demonstrates that failures and subsequent uncontainments result from a wider variety of reasons than previously believed. The causal factors for these uncontainments include maintenance, design deficiencies, manufacturing defects, corrosion, foreign object damage, etc. The FAA has determined that even with the best available strategies for addressing the root cause of engine failures, the FAA expects that new failure modes and failure sequences could exist. As a result, the FAA anticipates further challenges to the TEC containment structure, and has determined that the necessary containment modifications must be implemented through an AD as proposed.
In response to the comment that the root cause of all but one of the 64 referenced uncontained events are addressed by current mandatory action, the FAA does not concur. Additional review of the TEC penetration history reveals multiple incidents in which the root cause was undetermined, or in which no mandatory action by AD is required, or in which operators inadvertently did not comply with AD action, or in which improper repair or inspection was performed on certain engine components.
One commenter states that a probabilistic risk assessment accomplished by PW in October 1995 concludes that there is insufficient risk to mandate TEC modification. The FAA does not concur. The risk assessment performed by PW is a structured approach that enables the FAA to better assess and target critical areas and prioritize resources. It is also necessary to emphasize that risk assessment is not the only means of determining the need for mandatory corrective action, and that other parameters such as incidence rate, failure modes, restoration of certification basis, and basic engineering judgment are also utilized. The FAA has determined that for the TEC penetration issue all these other factors result in the need to issue an AD.
One commenter states that the FAA cost assessment of approximately $2,500 per engine to accomplish the proposed actions is based on the accomplishment of the option to weld shields to provide increase wall thickness. For some operators this is not a preferred option. The FAA concurs in part. The FAA has provided industry three options for compliance with the proposed AD. These options, in terms of decreasing cost, are as follows: a new thick wall TEC, a modified TEC with a new, thicker "P" flange, and finally welding on containment shields. Several operators have expressed concern with the durability of the welded containment shields option and take exception to the fact that the FAA utilized this option for the AD cost assessment. This operator plans to utilize one of the more costly methods for compliance with the AD. The FAA has reviewed all three options for enhanced containment and concludes that all three satisfy Part 33 of the Federal Aviation Regulations (FAR) (14 CFR part 33) requirements. The FAA performed the cost assessment utilizing the containment shield option since it has the least economic impact, and the FAA has reason to believe that the majority of operators will utilize this option, which has sound design and durability in accordance with FAR Part 33. The FAA understands that a new case would have greater longevity, and that the new "P" flange may be necessary when the existing "P" flange is no longer serviceable. In conclusion, this AD leaves it to the discretion of the operator the choice of option and provides all three options as approved type designs.
One commenter states that the containment shields are not an acceptable option, due to the fact that the shields could lead to corrosion of the TEC inner wall, which could compromise the structural integrity of the TEC. The FAA does not concur. The FAA has performed a thorough technical review of the proposed containment shields. As part of this review, multiple TECs were returned from service and have had their shields removed with subsequent sectioning of the case wall and shields for evaluation of corrosion extent. In this review no case walls were found with corrosion that compromised case wall thickness. In addition, no residual material was found that would suggest entrapment of foreign substances. The shields themselves also exhibited no corrosion that compromises type design wall thickness. This commenter states that the current cleaning and inspection procedures may have the potential for entrapment of cleaning and inspection solutions between the case wall and containment shields. The FAA has studied this concern and does not believe this is a problem. The FAA has determined that the containment shields are attached with a stitch weld, which will allow for sufficient purging of potentially corrosive solutions. When the TECs were sectioned in the evaluation, no residual deposits of cleaning or inspection solutions were found. However, to assure that corrosion due to potential entrapment of cleaning or inspection fluids is mitigated, the manufacturer is developing enhanced inspection and cleaning procedures in the engine overhaul manual.
One commenter states that they hold two Supplemental Type Certificates (STCs) that provide for modification of the TEC by the installation of a thicker containment wall, and requests inclusion of these STCs as a means of compliance to the AD. The FAA concurs andhas revised this final rule accordingly.
One commenter states that the inclusion of an STC in the AD as an alternative method of compliance gives the STC holder an unfair marketing advantage. The commenter requests that their company approved repair be listed in the text of the AD with the STC. The FAA does not concur. The AD identifies all known type designs and, as such, the STC is an FAA-approved type design. The commenter does not hold a design approval and therefore cannot be listed as a method of compliance to this AD. The commenter is listed in the PW SB as a source acceptable to PW for performing the approved repair. Therefore, the FAA would consider them an acceptable source for repair.
One commenter states that due to variations in incidence rate for uncontained TEC penetrations by engine model, i.e., JT9D-7, JT9D-7Q, and JT9D-7R4, that the FAA should adjust the proposed AD to be engine model specific. The FAA does not concur. The FAA finds that any variation in incident rate is not a significant enough factor to warrant providing a model-specific inspection interval.
Since issuance of the NPRM, the FAA has received a report that certain PW JT9D-7R4 TECs were modified improperly. These TECs have a soft material condition, which renders them incapable of properly containing debris, as required by this AD. These TECs were modified to incorporate a replacement "P" flange and case wall in accordance with PW SB No. JT9D-7R4-72- 513, Revision 3, November 13, 1996, or prior revisions. This final rule AD adds a paragraph to the compliance section requiring heat treatment of all TECs modified in accordance with PW SB No. JT9D-7R4-72-513, Revision 3, November 13, 1996, or prior revisions, in accordance with PW SB No. JT9D-7R4-72-534, dated October 18, 1996.
In addition, PW has issued SB No. 6157, Revision 1, dated July 17, 1996, which only differs from the original by adding additional repair stations. This final rule AD references Revision1 of this SB.
After careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of the rule with the changes described previously. The FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD.
There are approximately 2,748 engines of the affected design in the worldwide fleet. The FAA estimates that 740 engines installed on aircraft of U.S. registry will be affected by this AD, that it will take approximately 14 work hours per engine to accomplish the required actions, and that the average labor rate is $60 per work hour. Required parts will cost approximately $1,404 per engine. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $1,660,560.
The regulations adopted herein will not have substantial direct effects on the States, on the relationship between the nationalgovernment 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 final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment.
For the reasons discussed above, I certify that this action (1) is not a "significant regulatory action" under Executive Order 12866; (2) is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) 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 final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it 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, Incorporation by reference, Safety.
Adoption of the Amendment
Accordingly, pursuant to 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 USC 106(g), 40113, 44701. 39.13 - [AMENDED]
2. Section 39.13 is amended by adding the following new airworthiness directive: