[Federal Register Volume 63, Number 110 (Tuesday, June 9, 1998)]
[Rules and Regulations]
[Pages 31340-31345]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-15086]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 97-ANE-05; Amendment 39-10563; AD 98-12-07]
RIN 2120-AA64


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 Pratt & Whitney JT8D series 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 amendment shortens the 
inspection interval for certain low utilization disks. This amendment 
is prompted by reports of an additional uncontained 9th stage HPC disk 
failure due to corrosion pitting. The actions specified by this 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.

DATES: Effective August 10, 1998.
    The incorporation by reference of Pratt & Whitney Alert Service 
Bulletin No. 6038, Revision 5, dated August 17, 1994, as listed in the 
regulations, was approved previously by the Director of the Federal 
Register as of November 28, 1994 (59 FR 49175, September 27, 1994).

ADDRESSES: The service information referenced in this AD 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 Federal Aviation Administration (FAA), New England 
Region, Office of the Regional 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: 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: A proposal to amend part 39 of the Federal 
Aviation Regulations (14 CFR part 39) by superseding airworthiness 
directive (AD) 94-20-01, Amendment 39-9020 (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 was published in the Federal Register on September 17, 1997 (62 
FR 48800). That action proposed the same record search and inspection 
program but on a more conservative inspection schedule, and that low 
utilization disks, regardless of the disk coating, would have to be 
inspected at an interval of 7 years since new, replate, or corrosion 
(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 remained unchanged.
    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the comments received.
    Four commenters, comprising of 3 operators and the manufacturer, 
state that the proposed superseding rule should be withdrawn, based on 
the manufacturer's risk analysis, the lack of a defined unsafe 
condition, the lack of technical substantiation of the rule, and the 
belief that the current management plan is adequate to address the HPC 
disk corrosion issue. The FAA does not concur. The National 
Transportation Safety Board (NTSB) has determined from their 
investigation of the December 1995 accident that the most probable 
cause of the HPC disk failure was a fatigue crack which originated at a 
corrosion pit. The failed disk was last stripped of its protective 
coating and replated 8 years prior to the failure. The current AD and 
management plan requires reinspection of the disk at 10 year intervals. 
Therefore, the unsafe condition has been identified as the failure of a 
low utilization HPC disk prior to its currently mandated inspection 
interval. Risk analysis is used to develop a management plan to lower 
the probability of future events from occurring and cannot preclude a 
future event from occurring. The FAA establishes its confidence in the 
manufacturer's risk assessment by thoroughly reviewing the assumptions 
and modeling involved in developing the risk values. Although the FAA 
concurs that the manufacturer's risk assessment produces risk values 
that fall within typically acceptable limits, the FAA concludes that a 
more conservative corrective action is necessary. The acceptable risk 
limits are meant to be limits, and not typical values for allowable 
future risk. Establishing 7 years as the maximum inspection interval 
provides lowered risk without an onerous effect on the inspection and 
removal schedule, and, therefore, represents a desirable tradeoff. 
Furthermore, the reduced interval captures the concern of allowing a 
maximum inspection 25% in excess (10 years) of the recently-observed 
failure (8 years). While studies have determined that low utilization 
engines are more susceptible to corrosion because of the longer 
intervals between engine overhauls and the increased time spent 
stationary, subject to condensation, the FAA has determined that the 
statistical modeling of the onset and growth of a corrosion pit does 
not provide the level of confidence for the FAA to accept a longer 
interval. Therefore, the 7 year inspection interval was determined by 
the circumstances of the December 1995 accident. The disk failed 8 
years after replating, therefore in order to lower the risk of a 
similar event 7 years was chosen as the maximum inspection interval. 
This provides an adequate margin of safety against an incident 
occurring 8 years after replating.
    Three commenters state that the economic analysis is inadequate, as 
the costs don't take into account required early shop visits, costs 
associated with aircraft down time, and industry's inability to perform 
engine overhauls due to shortages of engine parts. The FAA does not 
concur as these costs do not directly stem from the AD's required 
actions. This AD does not require any additional action over and above 
the original AD; however, the FAA has chosen to adopt the original 
economic analysis for inclusion in this revision. The indirect costs 
associated with performing the maintenance actions required by this AD 
are not directly related to this proposed rule, and, therefore, are not 
addressed in the economic analysis for this rule. A full cost analysis 
for each AD, including such indirect costs, is not necessary since the 
FAA has already performed a cost benefit analysis when adopting the

[[Page 31341]]

part 33, airworthiness requirements to which these engines were 
originally certificated. A finding that an AD is warranted means that 
the original design no longer achieves the level of safety specified by 
those airworthiness requirements, and that other required actions are 
necessary, as in this case, stripping, corrosion inspecting and 
recoating or removing HPC disks. Because the original level of safety 
was already determined to be cost beneficial, these additional 
requirements needed to return the engine to that level of safety do not 
add any additional regulatory burden, and, therefore, a full cost 
analysis would be redundant and unnecessary.
    Two commenters state that the years since last inspection (YRSLI) 
criteria has been removed from the AD. The FAA concurs with the 
following exception. The years since last corrosion inspection was in 
the original AD as a one-time relief to operators who may have recently 
installed a disk and had not replated, but had performed a corrosion 
inspection. It was intended as a one-time only category for a disk and 
is not intended for repetitive inspections. The FAA concludes, however, 
that the original intent of YRSLI should remain intact and will change 
the compliance accordingly, but has reduced in this final rule the 
compliance interval of YRSLI by 3 years to be consistent with the 3 
year compliance interval reduction for years since new, replated, or 
corrosion inspected (YRSNRC).
    One commenter states that the mixed utilization disks category has 
been removed from the AD, as high utilization disks that become low 
utilization disks in the current AD receive a 40% time credit for the 
years they are operated as high utilization disks. The FAA concurs and 
has added to this final rule the time credit for disks that are 
operated as high utilization disks and then become low utilization 
disks. Low utilization disks that become high utilization disks must 
remain in the low utilization category until replated, and thus receive 
no time credit for time spent as a high utilization disk.
    One commenter states that engines will require immediate removal 
upon publication of the AD. The FAA does not concur. The FAA has 
considered the impact on industry from immediate removals of engines 
upon publication of the AD. Since this superseding AD contains the 
requirements of the current AD, only engines that are not currently in 
compliance with AD 94-20-01 should require immediate removal upon 
publication of this AD. Engines that fall outside of the new 
reinspection interval are given a reasonable drawdown period before 
compliance is required. Operators finding that immediate removal of 
engines is required may apply for relief through the procedures 
contained in the AD allowing for approval of an alternate method of 
compliance or an adjustment to the compliance time.
    One commenter states that they will follow the FAA-approved data 
contained in the PW Centralized and Coordinated Telecommunications 
Utility System (CACTUS) wire dated January 1, 1997. The FAA does not 
concur. Operators are reminded that PW's CACTUS wire is not FAA-
approved data. It is simply PW's method of communicating their 
recommendations to their operators. Further, FAA approval of 
maintenance plans does not constitute approval of an alternate method 
of complying with actions required by an AD. The exclusive procedure 
for seeking approval of an alternate method of compliance is provided 
in the AD.
    One commenter requests that previous alternative methods of 
compliance (AMOCs) should be applicable to this AD. The FAA concurs in 
part. The AMOCs to this AD are not intended to be different from the AD 
which it is superseding; however, the intervals for compliance are 
being adjusted by this AD. Therefore, approved AMOCs to AD 94-20-01 are 
approved for this AD, but adjustments to compliance times which were 
approved for 94-20-01 are not approved for this AD.
    One commenter requests clarification of partial year calculations. 
The FAA concurs in part. The FAA agrees that a partial year calculation 
of utilization rate is acceptable if a disk enters service at a time 
other than an operator's calculation interval. However, the FAA does 
not concur that a note is necessary in the AD to clarify this as it 
would unduly add to the complexity of the AD and that individual 
questions of this nature can best be handled on an individual basis.
    Five commenters concur with the rule as proposed.
    New part numbers compressor disks have been introduced by PW and 
approved for use by the FAA. However, these disks also require a 
corrosion inspection for all of the same reasons stated in the NPRM and 
this AD. Not adding the additional part numbers to the NPRM was an 
unintentional oversight. Since the introduction of the new part numbers 
was only introduced last year, no drawdown interval is specified or 
required. The addition of paragraph (d)(5) in the final rule poses no 
undo burden on operators and meets the intent of the NPRM.
    In addition, the FAA has clarified the phrasing in the compliance 
section of this AD to better explain the requirements for corrosion 
inspections.
    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 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 fleetwide 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. For the purposes of this cost analysis only, 
the FAA has conservatively estimated that 69% of the removed low 
utilization engines would require replacing the disks inspected. The 
FAA assumed that 3 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 superseding 
AD is based on the increased inspections of some low utilization disks. 
The FAA estimates 31% of the low utilization disks require an 
additional inspection. The cost of these additional inspections is 
estimated to be $4,426,658.
    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

[[Page 31342]]

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. 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, 
Amendment 39-10563, to read as follows:

98-12-07  Pratt & Whitney: Amendment 39-10563. Docket 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 (j) 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 these disks as high 
utilization disks 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, strip protective coating, 
corrosion 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 or Table B of this AD, whichever occurs later.

[[Page 31343]]



 Table A.--Years Since New, Recoated, or Corrosion Inspection (YRSNRC) 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, recoated or corrosion inspected                                                            
                        (YRSNRC)                                 Remove to inspect and recoat or replace        
----------------------------------------------------------------------------------------------------------------
Less than or equal to 5................................  By 7 YRSNRC.                                           
Greater than 5 but less than or equal to 6.............  Within 24 months.                                      
Greater than 6 but less than or equal to 7.............  Within 18 months.                                      
Greater than 7 but less than or equal to 8.............  Within 15 months.                                      
Greater than 8 but less than or equal to 9.............  Within 12 months.                                      
Greater than 9 but less than or equal to 10............  Before reaching 10 YRSNRC.                             
Greater than 10........................................  Before further flight.                                 
----------------------------------------------------------------------------------------------------------------


  Table B.--Years Since Last Non-Corrosion Inspection (YRSLI) 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 last non-corrosion inspection prior to November                                                     
                      28, 1994 (YRSLI)                             Remove to inspect and recoat or replace      
----------------------------------------------------------------------------------------------------------------
Less than or equal to 3....................................  By 5 YRSLI.                                        
Greater than 3 but less than or equal to 5.................  Within 24 months.                                  
Greater than 5 but less than or equal to 6.................  Within 18 months.                                  
Greater than 6 but less than or equal to 7.................  Within 12 months.                                  
Greater than 7 but less than or equal to 8.................  Before reaching 8 YRSLI.                           
Greater than 8.............................................  Before further flight.                             
----------------------------------------------------------------------------------------------------------------

    (2) For Nickel Cadmium coated disks listed by P/N in Chart C of 
PW ASB No. 6038, Revision 5, dated August 17, 1994, strip protective 
coating, corrosion 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 or Table D of this AD, whichever 
occurs later.

  Table C.--YRSNRC Inspection Interval for Low Utilization Disks--NiCad Coated Disks From Chart C of PW ASB No. 
                                     6038, Revision 5, Dated August 17, 1994                                    
----------------------------------------------------------------------------------------------------------------
    Years since new, recoated or corrosion inspected                                                            
                        (YRSNRC)                                 Remove to inspect and recoat or replace        
----------------------------------------------------------------------------------------------------------------
Less than or equal to 5................................  By 7 YRSNRC.                                           
Greater than 5 but less than or equal to 6.............  Within 24 months.                                      
Greater than 6 but less than or equal to 7.............  Within 21 months.                                      
Greater than 7 but less than or equal to 8.............  Within 18 months.                                      
Greater than 8 but less than or equal to 9.............  Within 15 months.                                      
Greater than 9 but less than or equal to 10............  Within 12 months.                                      
Greater than 10 but less than or equal to 11...........  Before reaching 11 YRSNRC.                             
Greater than 11........................................  Before further flight.                                 
----------------------------------------------------------------------------------------------------------------


  Table D.--YRSLI Inspection Interval for Low Utilization Disks--NiCad Coated Disks From Chart C of PW ASB No.  
                                     6038, Revision 5, Dated August 17, 1994                                    
----------------------------------------------------------------------------------------------------------------
Years since last non-corrosion inspection prior to November                                                     
                      28, 1994 (YRSLI)                             Remove to inspect and recoat or replace      
----------------------------------------------------------------------------------------------------------------
Less than or equal to 4....................................  By 6 YRSLI.                                        
Greater than 4 but less than or equal to 6.................  Within 24 months.                                  
Greater than 6 but less than or equal to 7.................  Within 18 months.                                  
Greater than 7 but less than or equal to 8.................  Within 12 months.                                  
Greater than 8 but less than or equal to 9.................  Before reaching 9 YRSLI.                           
Greater than 9.............................................  Before further flight.                             
----------------------------------------------------------------------------------------------------------------

    (3) For Aluminide coated disks listed by P/N in Chart B of PW 
ASB No. 6038, Revision 5, dated August 17, 1994, strip protective 
coating, corrosion inspect, and recoat or remove from service in 
accordance with PW JT8D Engine Manual, P/N 481672, at the time 
intervals specified in Table E or Table F of this AD, whichever 
occurs later.

Table E.--YRSNRC 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, recoated or corrosion inspected (YRSNRC)         Remove to inspect and recoat or replace      
----------------------------------------------------------------------------------------------------------------
Less than or equal to 5....................................  By 7 YRSNRC.                                       

[[Page 31344]]

                                                                                                                
Greater than 5 but less than or equal to 6.................  Within 24 months.                                  
Greater than 6 but less than or equal to 7.................  Within 18 months.                                  
Greater than 7 but less than or equal to 8.................  Within 12 months.                                  
Greater than 8 but less than or equal to 9.................  Before reaching 9 YRSNRC.                          
Greater than 9.............................................  Before further flight.                             
----------------------------------------------------------------------------------------------------------------


 Table F.--YRSLI 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 last non-corrosion inspection prior to November                                                     
                      28, 1994 (YRSLI)                             Remove to inspect and recoat or replace      
----------------------------------------------------------------------------------------------------------------
Less than or equal to 2....................................  By 4 YRSLI.                                        
Greater than 2 but less than or equal to 4.................  Within 24 months.                                  
Greater than 4 but less than or equal to 5.................  Within 18 months.                                  
Greater than 5 but less than or equal to 6.................  Within 12 months.                                  
Greater than 6 but less than or equal to 7.................  Before reaching 7 YRSLI.                           
Greater than 7.............................................  Before further flight.                             
----------------------------------------------------------------------------------------------------------------

    (4) For all other low utilization stage 7 through stage 12 HPC 
disks, strip protective coating, corrosion inspect, and recoat or 
remove from service in accordance with the PW JT8D Engine Manual, P/
N 481672, prior to 7 years since new, recoated, or corrosion 
inspected (YRSNRC).
    (5) For disks that are categorized as high utilization and 
subsequently entered low utilization service, YRSNRC can be adjusted 
as follows and applied to Table A, Table C, and Table E of this AD:
    (i) Adjusted YRSNRC = (0.60)  x  (years utilized at a rate 
greater than or equal to 1,300 hours per year, and greater than or 
equal to 900 cycles per year) + (years classified as low 
utilization).
    (ii) Once a disk enters low utilization service it must remain 
in that category and an adjustment to YRSNRC cannot be made for any 
subsequent high utilization operation.
    (iii) Years Since Last Non-Corrosion Inspection prior to 
November 18, 1994 (YRSLI) is a one-time interval only and cannot be 
used as a repetitive interval.
    (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, a corrosion inspection is 
defined as performing an inspection in accordance with PW Engine 
Manual 481672, section 72-36-41, inspection 01 for stage 7 disks, 
section 72-36-42, inspection 02, for 8th stage disks, section 72-36-
43, inspection 02 for 9th stage disks, section 72-36-44, inspection 
02 for 10th stage disks, section 72-36-45, inspection 02 for 11th 
stage disks, section 72-36-46, inspection 02 for 12th stage disks.
    (h) For the purpose of this AD, part accessibility is defined as 
the removal of the disk from the engine and deblading of that disk.
    (i) 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.
    (j) 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. Alternate methods of 
compliance approved for AD 94-20-01 are approved for this AD; 
adjustments to compliance times approved for AD 94-20-01 are not 
approved for this AD.

    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.

    (k) 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.
    (l) The actions required by this AD shall be done in accordance 
with the following PW ASB:

----------------------------------------------------------------------------------------------------------------
          Document No.               Pages                   Revision                           Date            
----------------------------------------------------------------------------------------------------------------
PW ASB No. 6038................          1     5..................................  August 17, 1994.            
                                         2     Original...........................  August 5, 1991.             
                                         3     5..................................  August 17, 1994.            
                                       4-6     4..................................  July 13, 1994.              
                                      7-26     5..................................  August 17, 1994.            
Appendix A.....................      27-41     5..................................  August 17, 1994.            
Appendix B NDIP-803............       1-33     4..................................  July 13, 1994.              
Appendix to NDIP-803...........        1-2     4..................................  July 13, 1994.              
    Total Pages: 76.                                                                                            
----------------------------------------------------------------------------------------------------------------


[[Page 31345]]

The incorporation by reference of PW ASB No. 6038, Revision 5, dated 
August 17, 1994, was approved previously by the Director of the 
Federal Register as of November 28, 1994 (59 FR 49175, September 27, 
1994). Copies may be obtained from Pratt & Whitney, 400 Main St., 
East Hartford, CT 06108; telephone (860) 565-6600, fax (860) 565-
4503. Copies may be inspected at the FAA, New England Region, Office 
of the Regional 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.
    (m) This amendment becomes effective on August 10, 1998.

    Issued in Burlington, Massachusetts, on May 29, 1998.
Jay J. Pardee,
Manager, Engine and Propeller Directorate, Aircraft Certification 
Service.
[FR Doc. 98-15086 Filed 6-8-98; 8:45 am]
BILLING CODE 4910-13-U