[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
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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.
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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.
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[[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