[Federal Register Volume 61, Number 225 (Wednesday, November 20, 1996)]
[Rules and Regulations]
[Pages 58975-58978]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-28988]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 95-ANE-45; Amendment 39-9815; AD 96-23-10]
RIN 2120-AA64
Airworthiness Directives; Pratt & Whitney JT3D Series Turbofan
Engines
AGENCY: Federal Aviation Administration, DOT.
ACTION: Final rule.
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SUMMARY: This amendment adopts a new airworthiness directive (AD),
applicable to Pratt & Whitney (PW) JT3D series turbofan engines, that
requires inspection of steel high pressure compressor (HPC) disks for
corrosion, recoating or replating those disks, or replacing those disks
as necessary. This amendment is prompted by reports of a failure of a
PW JT8D steel HPC disk, which is similar in design to the PW JT3D steel
HPC disks. The actions specified by this AD are intended to prevent
steel HPC disk failure due to corrosion, which could result in an
uncontained engine failure and damage to the aircraft.
DATES: Effective January 21, 1997.
The incorporation by reference of certain publications listed in
the regulations is approved by the Director of the Federal Register as
of January 21, 1997.
ADDRESSES: The service information referenced in this AD may be
obtained from Pratt & Whitney, Publications Department, Supervisor
Technical Publications Distribution, M/S 132-30, 400 Main St., East
Hartford, CT 06108; telephone (860) 565-7700, fax (860) 565-4503. This
information may be
[[Page 58976]]
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: Barbara Caufield, Aerospace Engineer,
Engine Certification Office, FAA, Engine and Propeller Directorate, 12
New England Executive Park, Burlington, MA 01803-5299; telephone (617)
238-7146, 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) JT3D series
turbofan engines was published in the Federal Register on October 31,
1995 (60 FR 53337). That action proposed to require inspection of steel
high pressure compressor (HPC) disks, stages 10-15, for corrosion,
recoating or replating those disks, or replacing those disks as
necessary in accordance with PW Alert Service Bulletin (ASB) No. A6208,
Revision 2, dated July 7, 1995.
Interested persons have been afforded an opportunity to participate
in the making of this amendment. Due consideration has been given to
the comments received.
Twelve commenters state that the compliance time to accomplish the
AD should be extended. The commenters state that due to the complex
workscope, aircraft down time, high cost, severe economic and
operational burden, significant impact on parts procurement, and shop
availability, the compliance times need to be extended. Times suggested
range from four to seven years, or next shop visit, or at exposure.
Pratt & Whitney has updated their risk analysis based on new data
provided by operators and a study concerning disk fractures resulting
in uncontained events. Based on this update they have revised Alert
Service Bulletin (ASB) No. A6208, extending the threshold and drawdown
intervals. The FAA concurs in part. The FAA has reviewed and approved
the technical contents of PW ASB No. A6208, Revision 3, dated January
11, 1996, and therefore the compliance time will be extended to that
included in the ASB based on PW's risk analysis. Other intervals
proposed are not technically justified.
Nineteen commenters state that the cost estimate in the NPRM is too
low since that estimate does not include the cost of additional
maintenance required under Part 121 (additional parts that must be
replaced that are unrelated to the AD requirements); engine testing,
fuel, oil, transportation/shipping, aircraft downtime, etc. The FAA
does not concur. The FAA's cost estimate is based on information from
the engine manufacturer to remove and replace the engine, teardown and
replacement of a percentage of HPC disks, and engine buildup. It does
not include costs not directly associated with the AD, because those
costs result from other maintenance requirements. The compliance
schedule of this AD allows for operators to schedule the required
actions with other, normally scheduled maintenance, thereby minimizing
the direct costs of the AD.
Six commenters state that part availability and shop capacity are
not adequate for the fleet to perform the AD. There is only one source
for new parts, and the supplier will not be able to keep up with the
demand for new disks and other parts. Some operators will not be able
to obtain parts to meet AD requirements. Operators will be competing
for shop space at the limited number of repair shops during a
restricted period of time. The FAA does not concur. The manufacturer
has advised the FAA that parts will be available to meet demand. In
addition, the FAA has determined, based on repair station input, that
shop capacity over the extended compliance time of this AD will be
satisfactory.
Eleven commenters state that there have been no PW JT3D disk
failures due to corrosion, and therefore no flight safety problem
exists, and that the AD should be withdrawn. The FAA does not concur.
Although there have been no known PW JT3D series disk failures to date
attributable to corrosion, the risk analysis by PW shows that if
corrosion inspection is not accomplished in accordance with the
applicable Service Bulletins' schedules the probability of a disk
fracture is unacceptably high.
Eight commenters question using JT8D experience as the basis for
this AD, as no consideration was given to differences in engine
application: i.e., four-engine versus twin-engine; that the PW JT3D
disk is heavier, and therefore has adequate safety margin; and that the
PW JT3D disk operates at slower speeds, different temperatures and
pressures. The FAA concurs in part. The commenters are correct in that
AD action was initiated because of similarity between the engines;
however, the analysis to generate inspection intervals and drawdown
times used data specific to the PW JT3D series.
Four commenters suggest that PW test a JT3D disk to failure to
evaluate the need for an AD and to verify the failure mode. The FAA
does not concur. The FAA determined that an unsafe condition exists
based on an actual failure of a similarly designed disk and a risk
analysis using JT3D data. No further testing is necessary, and the FAA
has concluded that the actions required by this AD are necessary to
address that unsafe condition.
Two commenters request a meeting between FAA, PW, and industry. The
FAA does not concur. A meeting was held with PW and a group of
operators in August 1995 prior to the publication of the NPRM; PW
requested operator input data for risk analysis at that time.
Three commenters state that only limited numbers of JT3D disks were
analyzed by PW in their risk analysis. The FAA does not concur. Since
publication of the NPRM, PW updated their risk analysis based on
additional data supplied by JT3D operators and the new data confirms
the earlier findings.
Three commenters state that the FAA underestimated the number of
affected engines in the economic analysis, and that 6,000 engines
worldwide are affected, including military and foreign. The FAA does
not concur. The FAA does not include military engines in its economic
analyses; these only refer to the civilian fleet.
Two commenters state that the AD should take operators' maintenance
programs into consideration and give flexible compliance schedules
based on maintenance programs. Operators' current disk inspection and
maintenance practices call for inspection of HPC disks for corrosion,
recoating, replating, or replacement. The FAA does not concur. The
criticality of this inspection warrants that it be separate and
distinct from routine maintenance tasks.
One commenter states that the FAA should consider using half-life
inspection on life-limited parts in conjunction with studies conducted
on HPC disks (based on the NPRM's statement ``corrosion is more apt to
occur if the steel HPC disk is not recoated/replated during its life
span and retains original production protective coating/plating.'') The
FAA does not concur. The referenced statement from the NPRM is for
informational purposes only, and the compliance time is based on PW's
risk analysis, which takes into account many factors, including disk
geometry, stress distribution, critical corrosion pit depth, crack
propagation rates, and engine utilization rates.
One commenter states that the FAA should allow metallurgists
appointed by operators to explore available data from
[[Page 58977]]
PW and examine how the correlation between PW JT8D and JT3D disks were
achieved, as the commenter does not accept the manufacturer's
conclusions. The FAA does not concur. Operators were given the
opportunity to present differing findings during the meeting that was
held with PW and a group of operators in August 1995.
One commenter states that there is no need for the AD as industry
is currently complying with the ASB. The FAA does not concur.
Airworthiness directive action is necessary to ensure compliance.
One commenter states that they were not consulted by the FAA prior
to the issuance of the NPRM, that their operational service experience
with HPC disks was not taken into account, and, accordingly, the AD
should not issue. The FAA does not concur. The FAA, as a rule, does not
usually consult with individual operators to gather facts for the
development of an airworthiness directive. The FAA does, however,
consult with the manufacturer of the product and industry groups and
associations. For this AD, the FAA did solicit input from Pratt &
Whitney, who, in turn, solicited input from operators for inclusion in
the risk analysis.
Two commenters agree with the rule as proposed.
Since publication of the NPRM, the FAA has received additional
economic data from the manufacturer and has recalculated the economic
analysis to reflect this new information.
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 2,000 engines of the affected design in the
worldwide fleet. The FAA estimates that 1,000 engines installed on
aircraft of U.S. registry will be affected by this AD. Based on
domestic fleet-wide data, the FAA estimates that approximately 40%, or
400 engines, will be required to be removed at times other than
regularly scheduled maintenance to accomplish the AD's actions.
Approximately 16 work hours are necessary to remove and replace the
engine, and the average labor rate is $60 per work hour. Approximately
100 work hours are required to teardown and rebuild the engine. The FAA
estimates that approximately 15% of disks removed from engines will
need to be scrapped at a cost of $9,000 per engine. Based on these
figures, the total cost impact of the AD on U.S. operators is estimated
to be $33,384,000 over a 15-year period.
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. 106(g), 40113, 44701.
Sec. 39.13 [Amended]
2. Section 39.13 is amended by adding the following new
airworthiness directive:
96-23-10--Pratt & Whitney: Amendment 39-9815. Docket 95- ANE-45.
Applicability: Pratt & Whitney (PW) Models JT3D-1, -1A, -3, -3B,
-3C, -1-MC6, -1A-MC6, -1-MC7, -1A-MC7, -7, -7A turbofan engines,
installed on but not limited to Boeing 707 and 720 series aircraft
and McDonnell Douglas DC-8 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 (b) 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 steel high pressure compressor (HPC) disk failure due
to corrosion, which could result in an uncontained engine failure
and damage to the aircraft, accomplish the following:
(a) Inspect steel HPC disks, stages 10-15, for corrosion, recoat
or replate, or replace as necessary, in accordance with PW Alert
Service Bulletin (ASB) No. A6208, Revision 3, dated January 11,
1996, and the following schedule:
(1) For disks coated with PWA 110-2/-3 Aluminide (non top coat
system) and for disks with unknown coating or plating, as follows:
(i) Initially inspect, recoat or replate, or replace as
necessary, within 14 years since new or since last recoat or
replate, or within 36 months after the effective date of this AD,
whichever occurs later.
(ii) Thereafter, inspect, recoat or replate, or replace as
necessary, at intervals not to exceed 14 years since new or last
coating, if PWA 110-2/-3 Aluminide (non top coat system) is applied,
or not to exceed 15 years since new or last plating, if PWA 110-21/-
31 Aluminide (top coat system) or Nickel Cadmium (NI-CAD) plating is
applied.
(2) For disks coated with PWA 110-21/-31 Aluminide (top coat
system) or plated with NI-CAD, as follows:
(i) Initially inspect, recoat or replate, or replace as
necessary, within 15 years since new or since last replate, or
within 36 months after the effective date of this AD, whichever
occurs later.
(ii) Thereafter, inspect, recoat or replate, or replace as
necessary, at intervals not to exceed 14 years since new or last
coating, if PWA 110-2/-3 Aluminide (non top coat system) is applied,
or not to exceed 15 years since new or last plating, if PWA 110-21/-
31 Aluminide (top coat system) or Nickel Cadmium (NI-CAD) plating is
applied.
(3) For disks with unknown coating or plating, and unknown time
since last coating or plating; or for disks with known coating or
plating and unknown time since last coating or plating, as follows:
(i) Initially inspect, recoat or replate, or replace as
necessary, within 36 months after the effective date of this AD.
(ii) Thereafter, inspect, recoat or replate, or replace as
necessary, at intervals not to exceed 14 years since new or last
coating, if PWA 110-2/-3 Aluminide (non top coat system) is applied,
or not to exceed 15 years since new or last plating, if PWA 110-21/-
31 Aluminide (top coat system) or Nickel Cadmium (NI-CAD) plating is
applied.
(b) An alternative method of compliance or adjustment of the
compliance time that
[[Page 58978]]
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 2: Information concerning the existence of approved
alternative methods of compliance with this airworthiness directive,
if any, may be obtained from the Engine Certification Office.
(c) 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.
(d) The actions required by this AD shall be done in accordance
with the following PW ASB:
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Document No. Pages Revision Date
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A6208.......................................... 1 3 Jan. 11, 1996.
2 1 May 8, 1995.
3 3 Jan. 11, 1996.
4 1 May 8, 1995.
5-9 3 Jan. 11, 1996
10-18 1 May 8, 1995.
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Total Pages: 18.
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, Supervisor Technical Publications Distribution, M/S 132-
30, 400 Main St., East Hartford, CT 06108; telephone (860) 565-7700,
fax (860) 565-4503. 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.
(e) This amendment becomes effective on January 21, 1997.
Issued in Burlington, Massachusetts, on November 1, 1996.
James C. Jones,
Acting Manager, Engine and Propeller Directorate, Aircraft
Certification Service.
[FR Doc. 96-28988 Filed 11-19-96; 8:45 am]
BILLING CODE 4910-13-U
