AD 94-20-09

This amendment supersedes an existing airworthiness directive (AD), applicable to certain Pratt & Whitney (PW) JT8D series turbofan engines, that currently requires initial and repetitive inspections of installed third and fourth stage low pressure turbine (LPT) blade sets for blade shroud crossnotch wear, and removal of blade sets found with excessively worn blade shroud crossnotches. This amendment continues to require inspections, and removal, if necessary, of blade sets, but also requires, as a terminating action to the inspections: installation of improved LPT containment hardware, installation of an improved No. 6 bearing scavenge pump bracket bushing, and modification and remarking with a new identification number third and fourth stage LPT vanes with a reduced platform leading edge dimension. This amendment is prompted by reports of additional uncontained engine failures since publication of the current AD, and the availability of improved LPT containment hardware.The actions specified by this AD are intended to prevent damage to the aircraft resulting from engine debris following an LPT blade or shaft failure.

Final rule.

94-20-09 Pratt & Whitney: Amendment 39-9037. Docket 93-ANE-72. Supersedes AD 92-10-05, Amendment 39-8239.
Applicability: Pratt & Whitney (PW) Model JT8D-15A, -17A, and -17AR turbofan engines, installed on but not limited to Boeing 737 and 727 series aircraft, and McDonnell Douglas DC-9 series aircraft.
Compliance: Required as indicated, unless accomplished previously.
To prevent damage to the aircraft resulting from engine debris following a low pressure turbine (LPT) blade or shaft failure, accomplish the following:
(a) For engines that do not contain PW honeycomb third stage outer airseal, Part Number (P/N) 801931, 802097, 797594, or 798279, or Parts Manufacturer Approval honeycomb third stage outer airseal P/N PI9336 or P/N M2433, and fan exhaust inner front duct segment assemblies that are installed in accordance with PW Alert Service Bulletin (ASB) No. 6039, Revision 3, dated October 15, 1993, or earlier revisions, accomplish the following:
(1) Conduct initial and repetitive inspections on installed third and fourth stage LPT blade sets, and remove and replace with serviceable blade sets, as necessary, in accordance with the requirements of Part 2 of the Accomplishment Instructions of PW ASB No. A5913, Revision 6, dated October 15, 1993, as follows:
(i) Initially inspect the blade shroud crossnotches of the third stage LPT blade set when specified in paragraph (a)(1)(i)(A) or (a)(1)(i)(B) of this AD, whichever occurs later, as follows:
(A) Inspect within 3,000 cycles or 3,000 hours time in service, whichever occurs first, since new, since the last blade shroud crossnotch inspection specified in Section 72-53-12 of PW JT8D Engine Manual P/N 481672, or since the last blade shroud crossnotch repair that was accomplished per the requirements specified in Section 72-53-12 of PW JT8D Engine Manual P/N 481672; or
(B) Inspect within 500 cycles or 500 hours time in service, whichever occurs first, after the effective date of this AD.
(ii) Initially inspect the blade shroud crossnotches of the fourth stage LPT blade set when specified in paragraph (a)(1)(ii)(A) or (a)(1)(ii)(B) of this AD, whichever occurs later, as follows:
(A) Inspect within 3,000 cycles or 3,000 hours time in service, whichever occurs first, since new, since the last blade shroud crossnotch inspection specified in Section 72-53-13 of PW JT8D Engine Manual P/N 481672, or since the last blade shroud crossnotch repair that was accomplished per the requirements specified in Section 72-53-13 of the PW JT8D Engine Manual P/N 481672; or
(B) Inspect within 500 cycles or 500 hours time in service, whichever occurs first, after the effective date of this AD.
(iii) Thereafter, inspect the third and fourth stage LPT blade sets in accordance with the procedures and intervals specified in PW ASB No. A5913, Revision 6, dated October 15, 1993.
(2) At the next shop visit after the effective date of this AD; but not later than December31, 1999, 8,000 hours time in service after the effective date of this AD, or 7,000 cycles after the effective date of this AD; whichever occurs latest, install the improved inner front fan exhaust duct and associated hardware in accordance with Part A of the Accomplishment Instructions of PW ASB No. A6110, Revision 1, dated October 15, 1993.
(3) At the next access to the third stage turbine air sealing ring after the effective date of this AD, but not later than December 31, 1999, 8,000 hours time in service after the effective date of this AD or 7,000 cycles after the effective date of this AD, whichever occurs latest, install the improved third stage turbine air sealing ring and associated hardware in accordance with Part B of the Accomplishment Instructions of PW ASB No. A6110, Revision 1, dated October 15, 1993.
NOTE: Third stage turbine outer air seal, P/N M2533, is an acceptable alternative to PW P/N 811962 for compliance with this paragraph.
(4) At the next shop visit after the effective date of this AD, but not later than December 31, 1999, 8,000 hours time in service after the effective date of this AD or 7,000 cycles after the effective date of this AD, whichever occurs latest, install the improved No. 6 bearing scavenge pump bracket bushing in accordance with the Accomplishment Instructions of PW ASB No. A6131, dated August 24, 1993.
(5) For engines that do not incorporate PW SB No. 5859, Revision 3, dated January 22, 1991, or earlier revisions, accomplish the following: at the next accessibility to the third and fourth stage LPT vane cluster assemblies after the effective date of this AD, but not later than December 31, 1999, 8,000 hours time in service after the effective date of this AD or 7,000 cycles after the effective date of this AD, whichever is latest, remove material from the inner platform leading edge on third and fourth stage LPT vane and vane cluster assemblies, and reidentify these modified vanes in accordance with the Accomplishment Instructions of PW SB No. 5748, Revision 5, dated August 3, 1993.
(6) Accomplishment of the installations and modification required by paragraphs (a)(2), (a)(3), (a)(4), and (a)(5) of this AD constitutes terminating action to the inspections required by paragraph (a)(1) of this AD.
(b) For engines that do contain PW honeycomb third stage outer airseal, P/N 801931, 802097, 797594, or 798279, or Parts Manufacturer Approval honeycomb third stage outer airseal P/N PI9336 or P/N M2433, and fan exhaust inner front duct segment assemblies that are installed in accordance with PW ASB No. 6039, Revision 3, dated October 15, 1993, or earlier revisions, perform the installations and modifications required by paragraphs (a)(2), (a)(3), (a)(4), and (a)(5) of this AD at the times specified in those respective paragraphs.
(c) For the purpose of this AD, a shop visit is defined as an engine removal where engine maintenance entails separation of pairs of major mating engine flanges or the removal of a disk, hub, or spool at a maintenance facility that is capable of compliance with the requirements of this AD, regardless of other planned maintenance, except for field maintenance type activities performed at this maintenance facility in lieu of performing them on-wing or at another peripheral facility.
(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. 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: Information concerning the existence of approved alternative method of compliance with this AD, 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.
(f) The inspections and modification shall be done in accordance with the following service bulletins:

Document No.
Pages
Revision
Date
PW ASB No. A5913
1
6
October 15, 1993

2
4
February 20, 1992

3-8
6
October 15, 1993

9
4
February 20, 1992

10
6
October 15, 1993

11
4
February 20, 1992

12
6
October 15, 1993
Appendix A
1
6
October 15, 1993

2-3
5
August 10, 1992

4
2
September 28, 1990

5
6
October 15, 1993

6
Original
April 2, 1990

7
2
September 28, 1990

8-14
Original
April 2, 1990
Total pages: 26.

PW ASB No. A6110
1
1
October 15, 1993

2
Original
March 19, 1993

3-59
1
October 15, 1993
Total pages: 59.

PW ASB No. A6131
1-13
Original
August 24, 1993
Total pages: 13.

PW SB No. 5748
1
5
August 3, 1993

2
2
September 15, 1988

3-4
5
August 3, 1993

5-10
2
September 15, 1988

11-12
5
August 3, 1993

13-16
2
September 15, 1988

17-18
4
October 3, 1989
Total pages: 18.

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, 400 Main Street, East Hartford, CT 06108. 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.
(g) This amendment becomes effective on November 14, 1994.

On May 4, 1992, the Federal Aviation Administration (FAA) issued AD 92-10-05, Amendment 39-8239 (57 FR 23050, June 1, 1992), applicable to Pratt & Whitney (PW) JT8D-15A, -17A, and -17AR engines, to require initial and repetitive inspections of the third and fourth stage low pressure turbine (LPT) blade sets for excessively worn blade shroud crossnotches, and the removal of blade sets found with excessively worn blade crossnotches. That AD is not applicable, however, to PW JT8D-15A, -17A, and -17AR engines that contain the third and fourth stage LPT containment hardware installed in accordance with PW Alert Service Bulletin (ASB) No. 6039, Revision 1, dated February 20, 1992.
A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) by superseding AD 92-10-05, Amendment 39-8239 (57 FR 23050, June 1, 1992), was published in the Federal Register on December 28, 1993 (58 FR 68570). That action proposed to continue to require repetitive inspections of installed third and fourth stage LPT blade sets for blade shroud crossnotch wear, and removal of blade sets found with excessively worn blade shroud crossnotches. These inspections are not required, however, for PW JT8D-15A, -17A, and -17AR engines that contain the third and fourth stage LPT containment hardware installed in accordance with PW ASB No. 6039, Revision 3, dated October 15, 1993, or earlier revisions.
That notice of proposed rulemaking (NPRM) also proposed to require, however, for all engines, installation of improved third stage LPT containment hardware at the next access to the third stage LPT air sealing ring, but not later than December 31, 1998; installation of the improved fourth stage LPT containment hardware at the next shop visit, but not later than December 31, 1998; installation of the improved No. 6 bearing scavenge pump bracket bushing at the next shop visit, but not later than December 31, 1998; and modification and remarking with a new identification number third and fourth stage LPT vanes with a reduced platform leading edge dimension at the next shop visit, but not later than December 31, 1998. The installation of improved containment hardware would serve as terminating action for the repetitive inspections.
The actions would be required to be accomplished in accordance with the following service documents: PW ASB No. A5913, Revision 6, dated October 15, 1993, that describes the third and fourth stage LPT blade set inspection procedures and replacement requirements; PW ASB No. A6110, Revision 1, dated October 15, 1993, that describes procedures for installation of improved LPT containment hardware; PW ASB No. A6131, dated August 24, 1993, that describes procedures for installation of an improved No. 6 bearing scavenge pump bracket bushing; and PW SB No. 5748, Revision 5, dated August 3, 1993, that describes modification and remarking with a new identification number third and fourth stage LPT vanes with a reduced platform leading edge dimension.
Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.
The FAA received several comments that state that inspections and modifications are available that address the root cause of shaft fractures and blade failures, whereas the installation of the containment hardware does not, and should therefore not be mandated. The FAA does not concur. Currently available inspections and modifications only protect against known failure modes, whereas the containment hardware will diminish the severity of all failure modes, both known and unknown, by protecting the aircraft from damage due to uncontained engine debris.
One commenter states that the FAA's economic analysis does not reflect the true cost of the containment hardware. The FAA does not concur. The intent of the economic analysis is to quantify the total direct cost to operators of the proposed rule. The analysis does, however, account for engines currently equipped with the required parts, and the price for the required parts quoted in the proposed rule is actually an average value that reflects costs for these engines.
One commenter states that the FAA's economic analysis does not account for the increased fuel costs resulting from the added weight of the containment hardware. The economic analysis reflects the direct costs of performing the requirements of the AD. Since the FAA has determined that the AD is required to correct an unsafe condition found in engines of this type design, and, therefore, operators must perform the requirements of the AD in order to ensure the continued airworthiness of the engines they operate, a comparison of the costs of operating the engine with and without the required containment hardware would not be proper.
One commenter states that the definition of shop visit stated in the proposed rule encompasses many types of minoror peripheral maintenance activities where installation of the containment hardware cannot be accomplished, thus causing a forced induction into an overhaul facility. The FAA concurs. The shop visit definition has been revised to address this commenter's concern.
One commenter states that adopting separate rules for separate groupings of PW JT8D engine models in Docket Nos. 93-ANE-72 and 93-ANE-83 is not justified since both address the same safety concern. In addition, separating into two separate rules also avoids a major rule classification and thereby reduces the economic impact of each separate action. The FAA does not concur. The FAA issues airworthiness directives based on product type design, not based on a failure mode, the result of a failure mode, or the description of a safety concern. Therefore, it is quite possible, as in this case, that more than one AD will address the same or very similar issues as they apply to more than one type design or more than one variant of a type design. In addition, in this case, each AD docket number cited by the commenter proposed to supersede an existing AD. Therefore, the AD's need to remain separate to maintain consistency with the superseded AD's in order to simplify the tracking of compliance by PW JT8D operators. Further, the economic impact of both rules combined would amount to approximately $51,000,000, which is far below the threshold for declaring a combined AD a significant regulatory action under Executive Order 12886 or a significant rule under existing DOT regulatory policy.
The FAA received several comments that state that the FAA should evaluate PW JT8D engine models separately to determine if all models require the proposed actions to be accomplished, or if some models can be exempted from compliance due to differences in design or demonstrated operational safety. The FAA does not concur. Design differences between the various PW JT8D engine models were evaluated and no significant differences, other than low pressure rotor speed in the higher rated engines, were revealed that could impact containment capability. The increased low pressure rotor speeds are protected for in the design of the higher rated engines with the addition of a turbine shield, and the historical event data does not indicate that these higher low pressure rotor speeds result in a greater number of uncontained failures.
One commenter states that an alternative to the compliance end date of December 31, 1998, should be expressed in hours and cycles, with performance required as whichever occur later, to accommodate low utilization operators. The FAA concurs. The FAA performed a risk analysis to determine the inspection interval requirements and hourly and cyclic equivalents to the compliance end date were derived from that risk analysis. The FAA has added the hourly and cyclic equivalents to the AD.
The FAA received several comments that state that the compliance requirements should be revised to minimize economic impact due to major engine disassembly. Specifically, modification of the LPT vane cluster assemblies and installation of the No. 6 bearing scavenge pump bracket bushing could entail major engine disassembly depending on the scope of work performed at the next shop visit occurring after the effective date of the AD. The FAA concurs in part. The FAA has determined that the modification of the LPT vane cluster assemblies can be accomplished at the next part access and still meet safety objectives. However, the compliance requirements for the installation of the No. 6 bearing scavenge pump bracket bushing is still required at the next shop visit to achieve the desired level of safety.
The FAA received several comments that state that PMA 3rd stage outer air seal, Part Number (P/N) M2533, manufactured by McClain International, should be an acceptable alternative installation to the corresponding PW part, P/N 811962. The FAA concurs. Third stage turbine outer air seal, P/N M2533, has been granted FAA PMA approval, and therefore meets all applicable Federal Aviation Regulations and is directly interchangeable with PW P/N 811962. The AD has been revised to specify P/N M2533 as an acceptable installation.
One commenter states the PW JT8D-17AR engines should be exempted from the requirement to install the thicker third stage turbine outer air seal because these engines are already configured with a turbine shield for containment protection. The FAA does not concur. The PW JT8D-17AR engines require additional containment protection due to higher rated low pressure rotor speeds on these engine models. Therefore, both the thicker third stage turbine outer air seal and the turbine shield are required for these engine models.
The FAA received two comments that state that additional costs could be incurred due to lack of availability of the parts required by this AD. The FAA does not concur. The FAA has coordinated this AD closely with PW to ensure the availability of the required parts. In addition, PMA parts are specified in this AD as an acceptable alternative for PW parts.

One commenter concurs with the rule as proposed.
The FAA has extended the compliance end date to December 31, 1999, in order to maintain consistency with AD 94-20-08, Docket No. 93-ANE-83. In addition, the compliance requirement for modification of the LPT vane cluster assemblies has been revised to exempt engines that incorporate PW SB No. 5859, Revision 3, dated January 22, 1991, or earlier revisions.
In addition, the FAA has determined that inspections of the third and fourth stage LPT blade sets in accordance with the procedures and intervals described in PW ASB No. 5913, Revision 5, dated August 10, 1992; or PW ASB No. 5913, Revision 4, dated February 20, 1992, constitute acceptable alternative methods of compliance for the inspections required by paragraph (a)(1) of this AD.
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 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.
The FAA estimates that 944 engines installed on aircraft of U.S. registry will be affected by this AD, that it will take approximately an average of 4 work hours, based on fleet configuration mix, per engine to accomplish the required actions, and that the average labor rate is $55 per work hour. Required parts will cost approximately $7,235 per engine. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $7,037,520.
The regulations adopted herein will 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 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 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89. 39.13 - [AMENDED]
2. Section 39.13 is amended by removing Amendment 39-8239 (57 FR 23050, June 1, 1992) and by adding a new airworthiness directive, Amendment 39-9037, to read as follows: