[Federal Register Volume 62, Number 180 (Wednesday, September 17, 1997)]
[Proposed Rules]
[Pages 48799-48802]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-24799]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 97-ANE-05]
RIN 2120-AA64


Airworthiness Directives; Pratt & Whitney JT8D Series Turbofan 
Engines

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the supersedure of an existing 
airworthiness directive (AD), applicable to Pratt & Whitney JT8D series 
turbofan engines, that currently requires a determination of the 
utilization rate and coating type of the 7th, 8th, 9th, 10th, 11th, and 
12th stage high pressure compressor (HPC) disks, and removal, 
inspection for corrosion, and recoating of those HPC disks based on 
utilization rate. This action would shorten the inspection interval for 
certain low utilization disks. This proposal is prompted by reports of 
an additional uncontained 9th stage HPC disk failure due to corrosion 
pitting. The actions specified by the proposed AD are intended to 
prevent fracture of the HPC disks, which can result in uncontained 
release of engine fragments, inflight engine shutdown, and airframe 
damage.

DATE: Comments must be received by November 17, 1997.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), New England Region, Office of the Assistant Chief 
Counsel, Attention: Rules Docket No. 97-ANE-05, 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.
    The service information referenced in the proposed rule may be 
obtained from Pratt & Whitney, 400 Main St., East Hartford, CT 06108; 
telephone (860) 565-6600, fax (860) 565-4503. This information may be 
examined at the FAA, New England Region, Office of the Assistant Chief 
Counsel, 12 New England Executive Park, Burlington, MA.

FOR FURTHER INFORMATION CONTACT: Christopher Spinney, Aerospace 
Engineer, Engine Certification Office, FAA, Engine and Propeller 
Directorate, 12 New England Executive Park, Burlington, MA 01803-5299; 
telephone (781) 238-7175, 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

[[Page 48800]]

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 97-ANE-05.'' 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 Assistant Chief Counsel, 
Attention: Rules Docket No. 97-ANE-05, 12 New England Executive Park, 
Burlington, MA 01803-5299.

Discussion

    On September 15, 1994, the Federal Aviation Administration (FAA) 
issued airworthiness directive AD 94-20-01, Amendment 39-9029 (59 FR 
49175, September 27, 1994), applicable to Pratt & Whitney (PW) JT8D-1, 
-1A, -1B, -7, -7A, -7B, -9, -9A, -11, -15, -15A, -17, -17A, -17R, and -
17AR turbofan engines, to require a record search, initial and 
repetitive on-wing and shop inspections to detect corrosion on high 
pressure compressor (HPC) disks, and removal from service of engines 
with HPC disks corroded beyond serviceable limits. That action was 
prompted by an investigation into an uncontained PW JT8D engine failure 
caused by severe corrosion on the 9th stage HPC disk. That condition, 
if not corrected, could result in fracture of the HPC disks, which can 
result in uncontained release of engine fragments, inflight engine 
shutdown, and airframe damage.
    Since the issuance of that AD, the FAA has received a report of a 
Boeing 737-232 powered by JT8D-7B turbofan engines that experienced an 
uncontained 9th stage HPC disk rupture in December 1995 during takeoff, 
which resulted in aircraft damage. The investigation determined that 
the 9th stage HPC disk rim failed due to a fatigue crack originating 
from a corrosion pit on the forward surface of the rim in the bottom of 
a compressor blade dovetail slot, which propagated in low cycle 
fatigue, and eventually fractured the hub. The investigation also 
identified extensive corrosion pitting in multiple sites that were 
concentrated in the outer web and rim areas of the disk.
    Airworthiness Directive 94-20-01 was published due to a similar 
uncontained PW JT8D series 9th stage HPC disk failure in which 
corrosion pitting was a factor. The investigation into this earlier 
failure also identified extensive corrosion on the failed 9th stage 
disk as well as the 8th and 10th stage disks. Corrosion pits as deep as 
0.020 inch and 0.060 inch in diameter were found in some areas of the 
ruptured 9th stage HPC disk. This earlier investigation concluded that 
PW JT8D HPC disks are more susceptible to severe corrosion when 
operating in a low utilization profile. Low utilization operating 
profiles can induce formation of condensation within the engine, 
thereby promoting corrosion scales and pits, which adversely affect the 
disk fatigue lives. As a compounding influence, low utilization rates 
imply longer on-wing calendar intervals and less frequent engine shop 
visits and module disassembles.
    This earlier investigation also evaluated the effectiveness of the 
protective coatings and lubricant/anti-gallant films used on the PW 
JT8D HPC disks. The FAA determined that varying degrees of corrosion 
resistance depends on the type of coating. As a result of this earlier 
investigation, the FAA issued AD 94-20-01, requiring a record search of 
the service history of the 8th, 9th, and 10th high pressure compressor 
disks, initial and repetitive on-wing and shop inspections to detect 
corrosion on HPC disks, and removal from service of engines with HPC 
disks corroded beyond serviceable limits. The inspection program of AD 
94-20-01 accounts for the variability in corrosion resistance and 
provides separate inspection instructions and criteria depending on the 
type of protective coating applied.
    This proposed AD would supersede AD 94-20-01 and require the same 
record search and inspection program but on a more conservative 
inspection schedule. The proposed AD would require the low utilization 
disks, regardless of the disk coating, to be inspected at an interval 
of 7 years since new, replated, or corrosion inspected (YRSNRC) in 
accordance with the engine manual. Currently, the inspection interval 
for low utilization disks is based on the disk coating and the maximum 
inspection interval ranges from 9 to 11 YRSNRC depending on the part 
number and the type of coating. The high utilization disk inspection 
interval remains unchanged.
    The FAA has reviewed and approved the technical contents of PW 
Alert Service Bulletin (ASB) No. 6038, Revision 5, dated August 17, 
1994, that describes on-wing and shop inspections to detect corrosion 
on HPC disks, and removal from service of HPC disks corroded beyond 
serviceable limits.
    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 supersede AD 94-20-01 to shorten the inspection 
interval for certain low utilization disks.
    There are approximately 11,119 engines of the affected design in 
the worldwide fleet. The FAA estimated that 6,815 engines installed on 
aircraft of U.S. registry were affected by AD 94-20-01, and 2 work 
hours would be necessary to determine the utilization rate and type of 
surface treatment. Based on domestic fleet-wide data, the FAA estimated 
that approximately 8.7% or 593 engines were considered to have low 
utilization rates. Approximately 8.6 work hours would be required to 
remove these engines from the aircraft, 500 work hours to tear down, 
deblade, and to reassemble the engine, and 8.6 work hours to reinstall 
the reassembled engines. The FAA estimated 69% of the removed engines 
would require scrapping the disks. The FAA assumed that three disks per 
engine may require replacement, and the cost of a new disk would be 
approximately $7,000. The average labor rate is $60 per work hour. 
Based on these figures, the total cost impact of AD 94-20-01 on U.S. 
operators was estimated to be $14,279,542. The cost increase between AD 
94-20-01 and this proposed AD is based on the increased inspections of 
some low utilization disks. The FAA estimates 31% of the low 
utilization disks would require an additional inspection. The cost of 
these additional inspections is estimated to be $4,426,658.
    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

[[Page 48801]]

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]

    2. Section 39.13 is amended by removing amendment 39-9029 (59 FR 
49175, September 27, 1994) and by adding a new airworthiness directive 
to read as follows:

Pratt & Whitney: Docket No. 97-ANE-05. Supersedes AD 94-20-01, 
Amendment 39-9029.

    Applicability: Pratt & Whitney (PW) JT8D-1, -1A, -1B, -7, -7A, -
7B, -9, -9A, -11, -15, -15A, -17, -17A, -17R, and -17AR turbofan 
engines installed on but not limited to Boeing 737 and 727 series, 
and McDonnell Douglas DC-9 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 (i) 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 fracture of the high pressure compressor (HPC) disks, 
which can result in uncontained release of engine fragments, 
inflight engine shutdown, and airframe damage, accomplish the 
following:
    (a) Within four months of the effective date of this AD, 
determine the fleet and sub-fleet average engine utilization rate 
for the 12 months of operations prior to August 17, 1994, the issue 
date of PW Alert Service Bulletin (ASB) No. 6038, Revision 5, in 
accordance with paragraph 2.A of PW ASB No. 6038, Revision 5, dated 
August 17, 1994.
    (1) For fleet or sub-fleet average utilization rates that are 
equal to or greater than 1,300 hours per year, and equal to or 
greater than 900 cycles per year, perform the following:
    (i) For engines or stage 7 through stage 12 HPC disks that were 
added to a fleet or subfleet after November 28,1994, and that were 
previously designated as low utilization disks in accordance with PW 
ASB No. 6038, Revision 5, dated August 17, 1994, comply with the 
requirements of paragraph (d) of this AD.
    (ii) Designate all other stage 7 through stage 12 HPC disks as 
high utilization disks and comply with the requirements of paragraph 
(b) of this AD.
    (2) For fleet or sub-fleet average utilization rates that are 
less than 1,300 hours per year or less than 900 cycles per year, 
within four months after the effective date of this AD, determine 
the utilization rate for each stage 7 through stage 12 HPC disk in 
accordance with paragraph 2.B.(1) of PW ASB No. 6038, Revision 5, 
dated August 17, 1994.
    (i) For each stage 7 through stage 12 HPC disk with an initial 
utilization rate equal to or greater than 1,300 hours per year, and 
equal to or greater than 900 cycles per year, designate this disk as 
a high utilization disk and inspect in accordance with paragraph (c) 
of this AD.
    (ii) For each stage 7 through stage 12 HPC disk with an initial 
utilization rate less than 1,300 hours per year or less than 900 
cycles per year, designate this disk as a low utilization disk and 
inspect in accordance with paragraph (d) of this AD.
    (iii) For each stage 7 through stage 12 HPC disk with an unknown 
initial utilization rate, designate this disk as a low utilization 
disk and inspect in accordance with paragraph (d) of this AD.

    Note 2: Once a disk is designated as low utilization, then it 
must retain this designation for the life of the disk or until 
recoated.

    (iv) For recoated or new disks, designate this disk as a high 
utilization disk and inspect in accordance with paragraph (c) of 
this AD.
    (b) For high average utilization fleets and sub-fleets, 
excluding those disks identified in paragraph (a)(1)(i) of this AD, 
perform the following for each stage 7 through stage 12 HPC disk in 
that fleet or sub-fleet:
    (1) Inspect, and recoat or replace if necessary, at the next 
part accessibility of the disk, in accordance with paragraph 
2.D.(1)(b) and Chart A of PW ASB No. 6038, Revision 5, dated August 
17, 1994.
    (2) Recalculate the fleet or sub-fleet average utilization rate 
at 12 month intervals after the previous date of utilization 
determination in accordance with paragraph 2.B of PW ASB No. 6038, 
Revision 5, dated August 17, 1994.
    (i) For fleet or sub-fleet average utilization rates that are 
equal to or greater than 1,300 hours per year, and equal to or 
greater than 900 cycles per year, continue to designate all stage 7 
through stage 12 HPC disks as high utilization disks and comply with 
the requirements of paragraph (b) of this AD.
    (ii) For fleet or sub-fleet average utilization rates that are 
less than 1,300 hours per year or less than 900 cycles per year, 
within four months of compliance with paragraph (b)(2) of this AD, 
determine the utilization rate for each stage 7 through stage 12 HPC 
disk in accordance with paragraph 2.B.(1) of PW ASB No. 6038, 
Revision 5, dated August 17, 1994, as follows:
    (A) For each stage 7 through stage 12 HPC disk with a 
utilization rate equal to or greater than 1,300 hours per year, and 
equal to or greater than 900 cycles per year, designate this disk as 
a high utilization disk and inspect in accordance with paragraph (c) 
of this AD.
    (B) For each stage 7 through stage 12 HPC disk with a 
utilization rate less than 1,300 hours per year or less than 900 
cycles per year, designate this disk as a low utilization disk and 
inspect in accordance with paragraph (d) of this AD.
    (C) For each stage 7 through stage 12 HPC disk with an unknown 
utilization rate, designate this disk as a low utilization disk and 
inspect in accordance with paragraph (d) of this AD.

    Note 3: Once a disk is designated as low utilization, then it 
must retain this designation for the life of the disk or until 
recoated.

    (c) For high utilization stage 7 through stage 12 HPC disks, 
perform the following:
    (1) Inspect, and recoat or replace if necessary, at the next 
part accessibility of the disk, in accordance with paragraph 
2.D.(1)(b) and Chart A of PW ASB No. 6038, Revision 5, dated August 
17, 1994.
    (2) Calculate the disk utilization rate at 12 month intervals 
after the previous date of utilization determination, or after 
installation of new or recoated disks, in accordance with paragraph 
2.B.(3) of PW ASB No. 6038, Revision 5, dated August 17, 1994.
    (i) For stage 7 through stage 12 HPC disks designated as high 
utilization in accordance with (c)(2), comply with the requirements 
of paragraph (c)(1) of this AD.
    (ii) For stage 7 through stage 12 HPC disks designated as low 
utilization in accordance with (c)(2), comply with the requirements 
of paragraph (d) of this AD.
    (d) For low utilization stage 7 through stage 12 HPC disks, 
perform the following:
    (1) For Nickel Cadmium coated disks listed by Part Number (P/N) 
in Chart B of PW ASB No. 6038, Revision 5, dated August 17, 1994, 
and Aluminide coated disks listed by P/N in Chart C of PW ASB 6038, 
Revision 5, dated August 17, 1994, inspect, and recoat or remove 
from service in accordance with PW JT8D Engine Manual, P/N 481672, 
at the time intervals specified in Table A of this AD.

[[Page 48802]]

    (2) For Nickel Cadmium coated disks listed by P/N in Chart C of 
PW ASB No. 6038, Revision 5, dated August 17, 1994, inspect and 
recoat or remove from service in accordance with PW JT8D Engine 
Manual, P/N 481672, at the time intervals specified in Table B of 
this AD.
    (3) For Aluminide coated disks listed by P/N in Chart B of PW 
ASB No. 6038, Revision 5, dated August 17, 1994, inspect and recoat 
or remove from service in accordance with PW JT8D Engine Manual, P/N 
481672, at the time intervals specified in Table C of this AD.

  Table A.--Inspection Interval for Low Utilization Disks NiCad coated  
   disks from Chart B of PW ASB No. 6038, Revision 5, dated August 17,  
    1994, and Aluminide coated disks from Chart C of PW ASB No. 6038,   
                    Revision 5, dated August 17, 1994                   
------------------------------------------------------------------------
  Years since new, replated or corrosion    Remove to inspect and recoat
   inspected (YRSNRC) per engine manual              or replace         
------------------------------------------------------------------------
Less than or equal to 5.0 YRSNRC..........  By 7 YRSNRC.                
Greater than 5.0 but less than or equal to  Within 24 months of the     
 6 YRSNRC.                                   effective date of this AD. 
Greater than 6 but less than or equal to 7  Within 18 months of the     
 YRSNRC.                                     effective date of this AD. 
Greater than 7 but less than or equal to 8  Within 15 months of the     
 YRSNRC.                                     effective date of this AD. 
Greater than 8 but less than or equal to 9  Within 12 months of the     
 YRSNC.                                      effective date of this AD. 
Greater than 9 but less than or equal to    Before reaching 10 YRSNRC.  
 10 YRSNRC.                                                             
Greater than 10 years.....................  Before further flight.      
------------------------------------------------------------------------


  Table B.--Inspection Interval for Low Utilization Disks NiCad coated  
disks from Chart C of PW ASB No. 6038, Revision 5, dated August 7, 1994.
------------------------------------------------------------------------
  Years since new, replated or corrosion    Remove to inspect and recoat
   inspected (YRSNRC) per engine manual              or replace         
------------------------------------------------------------------------
Less than or equal to 5.0 YRSNRC..........  By 7 YRSNRC.                
Greater than 5.0 but less than or equal to  Within 24 months of the     
 6 YRSNRC.                                   effective date of this AD. 
Greater than 6 but less than or equal to 7  Within 21 months of the     
 YRSNRC.                                     effective date of this AD. 
Greater than 7 but less than or equal to 8  Within 18 months of the     
 YRSNRC.                                     effective date of this AD. 
Greater than 8 but less than or equal to 9  Within 15 months of the     
 YRSNC.                                      effective date of this AD. 
Greater than 9 but less than or equal to    Within 12 months of the     
 10 YRSNRC.                                  effective date of this AD. 
Greater than 10 but less than or equal to   Before reaching 11 YRSNRC.  
 11 YRSNRC.                                                             
Greater than 11 years.....................  Before further flight.      
------------------------------------------------------------------------


Table C.--Inspection Interval for Low Utilization Disks Aluminide coated
   disks from Chart B of PW ASB No. 6038, Revision 5, dated August 17,  
                                  1994.                                 
------------------------------------------------------------------------
  Years since new, replated or corrosion    Remove to inspect and recoat
   inspected (YRSNRC) per engine manual              or replace         
------------------------------------------------------------------------
Less than or equal to 5.0 YRSNRC..........  By 7 YRSNRC.                
Greater than 5.0 but less than or equal to  Within 24 months of the     
 6 YRSNRC.                                   effective date of this AD. 
Greater than 6 but less than or equal to 7  Within 18 months of the     
 YRSNRC.                                     effective date of this AD. 
Greater than 7 but less than or equal to 8  Within 12 months of the     
 YRSNRC.                                     effective date of this AD. 
Greater than 8 but less than or equal to 9  Before reaching 9 YRSNRC.   
 YRSNC.                                                                 
Greater than 9 years......................  Before further flight.      
------------------------------------------------------------------------

    (e) For stage 7 through stage 12 HPC disks that have been 
recoated in accordance with paragraphs (b)(1), (c)(1), or (d)(1) of 
this AD, designate these disks as high utilization and perform the 
following:
    (1) For disks installed in an engine that is part of a high 
utilization fleet, comply with the requirements of paragraph (b) of 
this AD.
    (2) For disks installed in an engine that is part of a low 
utilization fleet, comply with the requirements of paragraph (c) of 
this AD.
    (f) For the purpose of this AD, recoat of an HPC disk is defined 
as removal and application of new plating or coating in accordance 
with Sections 72-36-41, Repair 02; 72-36-42, Repair 02; 72-36-43, 
Repair 03; 72-36-44, Repair 03; 72-36-45, Repair 03; or 72-36-46, 
Repair 03, as applicable, of PW JT8D Engine Manual P/N 481672.
    (g) For the purpose of this AD, part accessibility is defined as 
the removal of the disk from the engine and deblading of that disk.
    (h) For the purpose of this AD, a sub-fleet is defined as any 
individual aircraft or any portion of an operator's fleet that 
operates in a separate and unique route structure, characterized by 
different flight lengths, frequencies, or geographic location.
    (i) 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 4: Information concerning the existence of approved 
alternative methods of compliance with this airworthiness directive, 
if any, may be obtained from the Engine Certification Office.

    (j) 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.

    Issued in Burlington, Massachusetts, on September 10, 1997.
Mark C. Fulmer,
Acting Manager, Engine and Propeller Directorate, Aircraft 
Certification Service.
[FR Doc. 97-24799 Filed 9-16-97; 8:45 am]
BILLING CODE 4910-13-U