Airworthiness Directives; Pratt & Whitney JT8D Series Turbofan Engines

DEPARTMENT OF TRANSPORTATION

14 CFR Part 39

[Docket No. 93-ANE-72; Amendment 39-9037; AD 94-20-09]

Airworthiness Directives; Pratt & Whitney JT8D Series Turbofan

Engines

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: 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.

DATES: Effective November 14, 1994.

The incorporation by reference of certain publications listed in

the regulations is approved by the Director of the Federal Register as

of November 14, 1994.

ADDRESSES: The service information referenced in this AD may be

obtained from Pratt & Whitney, 400 Main Street, East Hartford, CT

06108. This information may be examined at the Federal Aviation

Administration (FAA), New England Region, Office of the Assistant Chief

Counsel, 12 New England Executive Park, Burlington, MA 01803-5299; or

at the Office of the Federal Register, 800 North Capitol Street, NW.,

suite 700, Washington, DC.

FOR FURTHER INFORMATION CONTACT: Mark A. Rumizen, Aerospace Engineer,

Engine Certification Office, FAA, Engine and Propeller Directorate, 12

New England Executive Park, Burlington, MA 01803-5299; telephone (617)

238-7137, fax (617) 238-7199.

SUPPLEMENTARY INFORMATION: 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 minor or 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-17R and -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 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.

Sec. 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:

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 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 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:

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Document No. Pages Revision Date

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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

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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.

Issued in Burlington, Massachusetts, on September 22, 1994.

Mark C. Fulmer,

Acting Manager, Engine and Propeller Directorate, Aircraft

Certification Service.

[FR Doc. 94-24201 Filed 10-12-94; 8:45 am]

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