[Federal Register Volume 59, Number 186 (Tuesday, September 27, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-23326]
[[Page Unknown]]
[Federal Register: September 27, 1994]
-----------------------------------------------------------------------
DEPARTMENT OF TRANSPORTATION
14 CFR Part 39
[Docket No. 92-ANE-44; Amendment 39-9029; AD 94-20-01]
Airworthiness Directives; Pratt & Whitney JT8D Series Turbofan
Engines
AGENCY: Federal Aviation Administration, DOT.
ACTION: Final rule.
-----------------------------------------------------------------------
SUMMARY: This amendment adopts a new airworthiness directive (AD),
applicable to Pratt & Whitney (PW) JT8D series turbofan engines, that
requires a determination of the utilization rate and coating type of
the 7th, 8th, 9th, 10th, 11th, and 12th high pressure compressor (HPC)
disks, and removal, inspection for corrosion, and recoating of those
HPC disks based on utilization rate. This amendment is prompted by an
investigation into an uncontained PW JT8D engine failure caused by
severe corrosion on the 9th stage HPC disk. 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 November 28, 1994.
The incorporation by reference of certain publications listed in
the regulations is approved by the Director of the Federal Register as
of November 28, 1994.
ADDRESSES: The service information referenced in this AD may be
obtained from Pratt & Whitney, Publications Department, 400 Main
Street, East Hartford, CT 06108. This information may be examined at
the Federal Aviation Administration (FAA), New England Region, Office
of the Assistant Chief Counsel, 12 New England Executive Park,
Burlington, MA; or at the Office of the Federal Register, 800 North
Capitol Street, NW., suite 700, Washington, DC.
FOR FURTHER INFORMATION CONTACT: Mark A. Rumizen, Aerospace Engineer,
Engine Certification Office, FAA, Engine and Propeller Directorate, 12
New England Executive Park, Burlington, MA 01803-5299; telephone no.
(617) 238-7137, fax (617) 238-7199.
SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal
Aviation Regulations (14 CFR part 39) to include an airworthiness
directive (AD) that is applicable to Pratt & Whitney (PW) JT8D series
turbofan engines was published in the Federal Register on July 27, 1993
(58 FR 40079). That action proposed 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. The inspections, and
replacement, if necessary, would be accomplished in accordance with PW
Alert Service Bulletin (ASB) No. 6038, Revision 3, dated May 8, 1992.
Interested persons have been afforded an opportunity to participate
in the making of this amendment. Due consideration has been given to
the comments received.
One commenter states that disks that are recoated when complying
with the inspection requirement of the AD should be zero-timed with
regard to the next inspection interval. The Federal Aviation
Administration (FAA) concurs. A paragraph has been added to the
compliance section that addresses recoated disks.
One commenter states that there have not been enough disk failures
to warrant issuance of an AD. The FAA does not concur. The need for an
AD is based on a determination that an unsafe condition exists that is
likely to exist in a product of the same type design. That
determination rests on many factors, including the risk and hazard
level of the failure mode, which in turn are based on several factors,
one of which is the number of failures that have occurred. Other data,
such as inspection data, analytical models, and potential consequences
are also considered when determining risk and hazard level. The FAA has
determined in these instances that an unsafe condition exists that is
likely to exist in engines of the same type design, and, therefore, an
AD is warranted.
The FAA received several comments that state that the borescope
inspection for corrosion assessment of Nickel-Cadmium (NiCad) disks is
unreliable and can cause unnecessary engine removals. The FAA concurs.
The borescope inspection for corrosion assessment of NiCad disks has
been eliminated and only in-shop inspections are now required. In
addition, high utilization disks require this inspection only at next
part access.
The FAA received two comments that state that the four month grace
period for the records search should be extended. The FAA concurs in
part. The records search is no longer specifically required, and can be
replaced by a simple utilization determination and an eddy current
probe inspection for coating type identification. In addition, the
utilization determination is based on a fleet or sub-fleet average. The
AD, however, requires that a utilization determination must be
conducted for each HPC disk within four months of the effective date of
this AD for low utilization operations. But, the FAA believes that it
is now a much simpler task.
The FAA received several comments that state that the AD does not
adequately address disks that have been used in both high and low
utilization operations. The FAA concurs. The utilization rate
determination now includes an adjustment for disks that have
experienced mixed utilization rates, and both an initial and a yearly
recalculation that will account for changes in utilization rate.
One commenter states that the AD should contain a provision to
allow for incorporation of the inspection requirements into the
operator's FAA-approved maintenance program. The FAA does not concur.
The criticality of the inspections required by the AD require that they
be separate and distinct from the operator's routine maintenance tasks.
The FAA received several comments that state that the records
search and inspection requirements of this AD pose an undue burden on
operators of PW JT8D engines. The FAA concurs in part. The records
search is no longer specifically required, and has been replaced by a
simpler utilization determination together with an eddy current probe
inspection for coating type identification. In addition, the
utilization determination is based on a fleet or sub-fleet average. The
borescope inspection has been eliminated, the disk removal (for
inspection) requirements have been relaxed based on additional analysis
and disk inspections, and high utilization disks, fleets, and sub-
fleets will not require a forced engine removal to comply with the AD.
The FAA received two comments that state that the compliance
schedule for disk inspections is complex and requires extensive
recordkeeping. The FAA concurs. The compliance schedule has now been
simplified by eliminating the borescope inspection and by requiring
high utilization operators to inspect the disks at the next access
regardless of coating type.
The FAA received two comments that state that the issuance of the
Final Rule should be delayed until additional analytical and
statistical analyses can be performed to further refine disk fracture
predictions and required inspection intervals. The FAA does not concur.
The FAA performed extensive additional analysis since the issuance of
the proposed rule which has resulted in the revised compliance
requirements discussed in the FAA's responses to several comments.
Based on this additional analysis, the FAA believes that the Final Rule
should not be delayed.
One commenter states that the cost to drill the borescope hole
would place an undue burden on the operator. The FAA concurs in part.
The borescope inspection has been eliminated from the AD and borescope
access is not specifically required. However, borescope access is
required if an operator elects to forgo a records search and elects to
use the eddy current probe to determine coating type.
One commenter states that the disk records do not always allow for
identification of the coating. The FAA concurs. The identification of
disk coating can now be accomplished by use of an eddy current probe.
One commenter states that the AD should allow for incorporation of
an engine heater/de-humidifier to be installed on low utilization
engines when not in operation. This type of device would reduce the
accumulation of moisture in the engine, which can cause disk corrosion.
The FAA concurs in part and does not dispute that an engine heater/de-
humidifier would probably reduce the moisture content in low
utilization engines. This type of device, however, would need to be
tested to produce data to quantify its effect on moisture and
associated disk corrosion. Since this data has not been submitted to
the FAA, it cannot be included in the AD.
One commenter agreed with the rule as proposed.
Since publication of the NPRM, the FAA has reviewed and approved
the technical contents of PW ASB No. 6038, Revision 5, dated August 17,
1994. This final rule AD references the latest revision of the ASB.
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 that include
elimination of the borescope inspection and associated tables, changes
to the compliance intervals, elimination of the records search,
addition of the optional eddy current probe inspection, addition of the
adjustment for mixed utilization, and simplification of the utilization
determination, are introduced in response to comments received to the
NPRM. The format of the compliance section is revised to incorporate
the above changes and to simplify the readability by eliminating
duplication of compliance instructions that are now included in PW ASB
6038, Revision 5, dated August 17, 1994. The FAA has determined that
these changes do not increase the economic burden on any operator,
however, the economic analysis has been recalculated to reflect the
total scope of the compliance program. The FAA has also determined that
the above changes do not compromise the safety impact of the compliance
program and do not increase the scope of the AD.
There are approximately 11,119 PW JT8D-1, -1A, -1B, -7, -7A, -7B, -
9, -9A, -11, -15, -15A, -17, -17A, -17R, and -17AR turbofan engines of
the affected design in the worldwide fleet. The FAA estimates that
approximately 6,815 engines installed on aircraft of U.S. registry will
be affected by this AD, and 2 work hours will be necessary to determine
the utilization rate and type of surface treatment. Based on domestic
fleet-wide data, the FAA estimates that approximately 8.7% or 593
engines are considered to have low utilization rates. Approximately 8.6
work hours will 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 estimates
69% of the removed engines will require scrapping the disks. The FAA
assumes that three disks per engine may require replacement, and the
cost of a new disk is approximately $7,000. The average labor rate is
$55 per work hour. Based on these figures, and a forecast 20-year
compliance program, the annual cost impact of the AD on U.S. operators
is estimated to be $1,308,958.
The regulations adopted herein will not have substantial direct
effects on the States, on the relationship between the national
government and the States, or on the distribution of power and
responsibilities among the various levels of government. Therefore, in
accordance with Executive Order 12612, it is determined that this final
rule does not have sufficient federalism implications to warrant the
preparation of a Federalism Assessment.
For the reasons discussed above, I certify that this action (1) Is
not a ``significant regulatory action'' under Executive Order 12866;
(2) is not a ``significant rule'' under DOT Regulatory Policies and
Procedures (44 FR 11034, February 26, 1979); and (3) will not have a
significant economic impact, positive or negative, on a substantial
number of small entities under the criteria of the Regulatory
Flexibility Act. A final evaluation has been prepared for this action
and it is contained in the Rules Docket. A copy of it may be obtained
from the Rules Docket at the location provided under the caption
ADDRESSES.
List of Subjects in 14 CFR Part 39
Air Transportation, Aircraft, Aviation safety, Incorporation by
reference, Safety.
Adoption of the Amendment
Accordingly, pursuant to the authority delegated to me by the
Administrator, the Federal Aviation Administration amends part 39 of
the Federal Aviation Regulations (14 CFR part 39) as follows:
PART 39--AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C.
106(g); and 14 CFR 11.89.
Sec. 39.13 [AMENDED]
2. Section 39.13 is amended by adding the following new
airworthiness directive:
94-20-01 Pratt & Whitney: Amendment 39-9029. Docket 92-ANE-44.
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.
Compliance: Required as indicated, unless accomplished
previously.
To prevent fracture of the high pressure compressor (HPC) disks,
that can result in uncontained release of engine fragments, inflight
engine shutdown, and airframe damage, accomplish the following:
(a) Within four months after the effective date of this
airworthiness directive (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 disks that are added to a fleet or subfleet
after the effective date of this AD, and that were previously
designated as low utilization disks in accordance with this AD,
comply with the requirements of paragraph (d) of this AD.
(ii) Designate all other stage 7 through 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 initial utilization rate for each stage 7 through 12 HPC disk in
accordance with paragraph 2.B.(1) of PW ASB No. 6038, Revision 5,
dated August 17, 1994. Determination of disk utilization in
accordance with PW ASB No. 6038, Revision 3, dated May 8, 1992,
constitutes an acceptable alternate method of compliance to
paragraph (a)(2) of this AD.
(i) For each HPC stage 7 through 12 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 HPC stage 7 through 12 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 HPC stage 7 through 12 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: 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 HPC stage 7 through 12 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 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 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 HPC stage 7 through 12 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 HPC stage 7 through 12 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 HPC stage 7 through 12 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: 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 HPC stage 7 through 12 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 HPC stage 7 through 12 disks designated as high
utilization in accordance with (c)(2), comply with the requirements
of paragraph (c)(1) of this AD.
(ii) For HPC stage 7 through 12 disks designated as low
utilization in accordance with (c)(2), comply with the requirements
of paragraph (d) of this AD.
(d) For low utilization HPC stage 7 through 12 disks, perform
the following:
(1) Determine the type of disk surface treatment for each HPC
stage 7 through 12 disk in accordance with paragraph 2.E. of PW ASB
No. 6038, Revision 5, dated August 17, 1994. Determination of type
of disk coating in accordance with PW ASB No. 6038, Revision 3,
dated May 8, 1992, constitutes an acceptable alternate method of
compliance to paragraph (d)(1) of this AD.
(2) Inspect, and recoat or remove from service, in accordance
with paragraph 2.D.(1)(c) and Chart A of PW ASB No. 6038, Revision
5, dated August 17, 1994.
(e) For HPC stage 7 through 12 disks that have been recoated in
accordance with paragraphs (b)(1), (c)(1), or (d)(2) 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, 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 operators 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. The
request should be forwarded through an appropriate FAA Principal
Maintenance Inspector, who may add comments and then send it to the
Manager, Engine Certification Office.
Note: Information concerning the existence of approved
alternative 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.
(k) The inspections, and replacement or recoating if necessary,
shall be done in accordance with the following service document:
------------------------------------------------------------------------
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- 1-2 4............. July 13, 1994.
803.
Total Pages:
76.
------------------------------------------------------------------------
This incorporation by reference was approved by the Director of
the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR
part 51. Copies may be obtained from Pratt & Whitney, Publications
Department, 400 Main Street, East Hartford, Connecticut 06108.
Copies may be inspected at the FAA, New England Region, Office of
the Assistant Chief Counsel, 12 New England Executive Park,
Burlington, MA; or at the Office of the Federal Register, 800 North
Capitol Street NW., suite 700, Washington, DC.
(l) This amendment becomes effective on November 28, 1994.
Issued in Burlington, Massachusetts, on September 15, 1994.
Jay J. Pardee,
Manager, Engine and Propeller Directorate, Aircraft Certification
Service.
[FR Doc. 94-23326 Filed 9-26-94; 8:45 am]
BILLING CODE 4910-13-P
