[Federal Register Volume 63, Number 219 (Friday, November 13, 1998)]
[Rules and Regulations]
[Pages 63393-63396]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-30332]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 98-ANE-21-AD; Amendment 39-10872; AD 98-23-07]
RIN 2120-AA64
Airworthiness Directives; Pratt & Whitney JT9D 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 certain Pratt & Whitney (PW) JT9D series turbofan
engines, that requires a one-time acid etch inspection of the turbine
exhaust case (TEC) wall between and on either side of the ``R'' and
``S'' rails in the engine mount lug area (top quadrant of the case) for
the presence of weld material, and if weld material is detected,
removal from service and replacement with serviceable parts. This
amendment is prompted by reports of weld rework performed in the outer
case wall of the TEC, in the mount lug fillet area, during original
production to address local under minimum wall thickness conditions
which have left the TEC's structural capability compromised. The
actions specified by this AD are intended to prevent TEC structural
failure under abnormal operating conditions, which could result in
reduced main mount load capability, engine separation from the wing and
subsequent loss of control of the aircraft.
DATES: Effective January 12, 1999.
The incorporation by reference of certain publications listed in
the regulations is approved by the Director of the Federal Register as
of January 12, 1999.
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; or at the Office of the Federal Register, 800 North
Capitol Street, NW., suite 700, Washington, DC.
FOR FURTHER INFORMATION CONTACT: Tara Goodman, Aerospace Engineer,
Engine Certification Office, FAA, Engine and Propeller Directorate, 12
New England Executive Park, Burlington, MA 01803-5299; telephone (781)
238-7130, fax (781) 238-7199.
[[Page 63394]]
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 certain Pratt & Whitney (PW)
Models JT9D-7, -7A, -7H, -7AH, -7F, -7J, -20, -20J, -7Q, -7Q3, -59A, -
70A, and -7R4D turbofan engines was published in the Federal Register
on May 7, 1998 (63 FR 25179). That action proposed to require at the
next removal of the TEC from the low pressure turbine case ``P'' flange
for maintenance after the effective date of this AD, a one-time acid
etch inspection of TEC wall between and on either side of the ``R'' and
``S'' rails in the engine mount lug area (top quadrant of the case) for
the presence of weld material, and if that material is detected,
removal from service and replacement with serviceable parts.
Interested persons have been afforded an opportunity to participate
in the making of this amendment. Due consideration has been given to
the comments received.
Risk Assessment
Several commenters question the risk assessment used to generate
the proposed rule. The FAA will address each comment individually and
provide responses.
Two commenters state that a Continued Airworthiness Assessment
Methodology (C.A.A.M.) analysis needs to be performed to validate the
risk analysis submitted by the manufacturer for this rulemaking. The
FAA does not concur. C.A.A.M. is a system of assessing and managing
risk that includes the use of quantitative risk analysis models. The
risk analysis submitted by the manufacturer to evaluate the subject
unsafe condition followed the C.A.A.M. procedure.
Two commenters indicate that utilizing data from one operator is
insufficient to establish an appropriate risk factor. The FAA does not
concur. The database of the one operator in question is extensive,
since it represents a substantial portion of the engine fleet and
includes detailed records of all inspections, and has been validated
repeatedly against full-fleet experience.
Two commenters object to the use of data from one operator based on
that operator's hour-to-cycle mission profile. The FAA does not concur.
Cracking in the mount lug area of the TEC is a function of high stress
and temperature operation on a cyclic basis, and is independent of
hours, time in service (TIS).
One commenter takes issue with the assumption of constant fleet
size and utilization. The FAA does not concur. The future rate of
utilization is subject to a variety of factors, including resale and
continued use of engines. The assumption of constant fleet size and
utilization has been consistently used in previous risk analyses,
therefore, this assumption allows comparison of this risk with other
unsafe conditions.
One commenter takes issue with the use of linear interpolation to
predict failures instead of using Weibull analysis. The FAA does not
concur. Weibull analysis was used to develop the failure distribution.
One commenter notes it is not apparent that an assessment for
incorrectly reading the acid etch is accounted for in the risk
analysis. The FAA does not concur. The probability of correctly
interpreting the macroetch results for the weld condition is high. This
factor does not significantly affect the results of the risk analysis.
One commenter postulates a lower risk of fan blade release coupled
with a TEC with welds or cracks. The FAA does not concur. The FAA finds
this calculation inaccurate because it: (1) includes only past
occurrences for its estimate of the percent of the fleet with TEC
cracks or welds and (2) it does not use the standard statistical
practice for calculating mean time between failure.
One commenter states that since there has never been a failure of
the TEC from a full blade out or rotor seizure, the risk analysis is in
question. The FAA does not concur. Corrective action does not need to
occur as a result of a serious event. The FAA has determined that an
unsafe condition exists and therefore this rulemaking is necessary as a
proactive approach to continued airworthiness.
Two commenters request the FAA direct PW to partner with the
operators to develop a risk assessment, which takes into consideration
specific data elements from the major affected operators to determine a
logical and true safety risk and to postpone rulemaking until such time
that this risk analysis can be reviewed. The FAA does not concur. The
FAA has determined that the risk assessment evaluated for this
rulemaking is appropriate. Since an unsafe condition has been
determined to exist and is likely to develop on other products of the
same type design, it is appropriate to issue this AD without further
delay.
Other Comments
Two commenters cite concerns about consistency for inspecting the
primary mount locations on the TEC for the JT9D-7A/7F/7J models and the
JT9D-20/20J models. The FAA concurs. Revision 1 of the SBs, referenced
in this final rule, have corrected the inconsistency among engine
models for the primary mount locations.
Two commenters request that the economic impact of the proposal be
revised to reflect case repairs and acquisition of new cases. The FAA
concurs. There are 1,125 engines installed on aircraft of U.S. registry
that would be affected by the inspection requirements of this AD. The
average labor rate is $60 per work hour and it would take approximately
1.4 work hours per engine to accomplish the acid etch inspection. For
the inspection, then, the estimated impact is $94,500. The cost of
replacement of a TEC found with welding in the primary mount lug area
is approximately $495,000 per TEC. Since this AD addresses 23 TECs that
are unaccounted for in the field, the estimated impact is $11,385,000.
Therefore the total estimated cost impact of this AD is $11,479,000.
One commenter notes that the proposed rule states the required
actions must be taken at the next removal of the TEC from the low
pressure turbine case ``P'' flange. If the phrase ``when the engine is
in the shop,'' were added it would provide for exchanging a TEC in the
hangar during an aircraft service. Normally when a TEC is replaced in
the hangar, an overhauled case is obtained from a vendor. However, on
occasion, a TEC is obtained from another engine and a small airline
needs this flexibility. The FAA concurs. The FAA has revised the shop
visit definition in the compliance section of this final rule to
induction of the engine into the shop for scheduled maintenance.
One commenter states that they are currently inspecting the TECs to
the original SB and the Internal Engineering Notice (IEN) noted in PW
All Operators Wire (AOW). The commenter requests the AD indicate the
original of SB 6322, A72-546 and IEN 97ECO56C as compliance with the
AD. The FAA concurs. In the interest of time to alert operators of the
need to conduct the inspection, PW issued an AOW citing the IEN number
97ECO56C which is used within PW to issue the original SB. The IEN for
Revision 1 to SB 6322 and A72-546 were issued before the NPRM was
released and provided better etching agents the operator can use for
the inspection and referenced acid etch inspection for only the primary
mount lug locations. Since complying with the original SBs is more
restrictive than Revision 1, this final rule has been revised to
reference the original issue of the affected SBs.
One commenter concurs with the rule as proposed.
[[Page 63395]]
Additional Technical Concerns
The following technical concerns were raised in comments to the
proposed rule, but do not request any specific changes to the rule as
proposed, however the FAA will answer these technical concerns.
One commenter asks if the full fan blade out test data was not
required for SB 4853 why is a full fan blade out test required to
evaluate welds in mount areas? The commenter also asks why is the
static deflection load test data presented to the FAA for welds in the
mount areas not admissible as substantiation, when PW considered static
load test data admissible for mount lug area modifications? The FAA
does not concur. The objective of SB 4853 is to address cracking in the
TEC struts and rails and does not address the case wall. Also, PW did
not submit data to substantiate weld repairs in the primary mount lug
areas, and no other design approvals allowing for weld repairs in the
primary mount lug areas have been issued by the FAA.
One commenter refers to AD 96-25-10 (Docket 95-ANE-57) that
requires JT9D TEC modification to increase the containment capability
and includes the option of welding doublers on the inside surface of
the TEC or welding a thicker replacement flange onto the case, and then
asks why is the FAA unconcerned about the TEC's ability to withstand a
full fan blade out or rotor seizure for a case that has a 360 degree
weld approximately 1.2'' away from the mount bosses? The FAA does not
concur. Welds associated with the P flange replacement and containment
shields are outside the high stress zone of the primary mount lug
locations.
Two commenters request that the Chromalloy ``strongback'' repair be
listed as a means for compliance with the AD. The FAA does not concur.
The repair has not been approved by the FAA nor does it provide an
alternate method of compliance to the AD as proposed. The AD method of
compliance is to perform an acid etch and conduct an inspection,
therefore the Chromalloy repair is considered outside the scope of this
AD.
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.
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:
98-23-07 Pratt & Whitney: Amendment 39-10872. Docket 98-ANE-21-AD.
Applicability: Pratt & Whitney (PW) Models JT9D-7, -7A, -7H, -
7AH, -7F, -7J, -20, -20J, -7Q, -7Q3, -59A, -70A, and -7R4D turbofan
engines. These engines are installed on but not limited to Boeing
747 and 767 series, McDonnell Douglas DC-10 series, and Airbus A300
and A310 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 (c) 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 turbine exhaust case (TEC) structural failure under
abnormal operating conditions, which could result in reduced main
mount load capability, engine separation from the wing and
subsequent loss of aircraft control, accomplish the following:
(a) At the next shop visit after the effective date of this AD,
accomplish the following in accordance with PW Alert Service
Bulletin (ASB) No. JT9D-A6322, Revision 1, dated August 13, 1998, or
Original, dated March 19, 1998, or ASB No. JT9D-7R4-A72-546,
Revision 1, dated August 13, 1998, or Original, dated March 19,
1998, as applicable:
(1) Perform a one-time acid etch inspection of TEC wall between
and on either side of the ``R'' and ``S'' rails in the engine mount
lug area (top quadrant of the case) for the presence of weld
material.
(2) If weld material is found, remove from service the TEC and
replace with a serviceable part.
(b) For the purpose of this AD, a shop visit is defined as the
induction of an engine into a shop for the purpose of maintenance.
(c) 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 request 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.
(d) 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.
(e) The actions required by this AD shall be done in accordance
with the following PW ASBs:
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Document No. Pages Revision Date
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JT9D-7R4-A72-546................. 1-4..................... 1....................... August 13, 1998.
[[Page 63396]]
5....................... Original................ March 19, 1998.
6-9..................... 1....................... August 13, 1998.
10, 11.................. Original................ March 19, 1998.
12-19................... 1....................... August 13, 1998.
Total Pages: 19
JT9D-7R4-A72-546................. 1-16.................... Original................ March 19, 1998.
Total Pages: 16.
A6322............................ 1-4..................... 1....................... August 13, 1998.
5-22.................... Original................ March 19, 1998.
23-29................... 1....................... August 13, 1998.
30, 31.................. Original................ March 19, 1998.
32-45................... 1....................... August 13, 1998.
Total Pages: 45.
A6322............................ 1-41.................... Original................ March 19, 1998.
Total Pages: 41.
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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, 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.
(f) This amendment becomes effective on January 12, 1999.
Issued in Burlington, Massachusetts, on November 5, 1998.
David A. Downey,
Assistant Manager, Engine and Propeller Directorate, Aircraft
Certification Service.
[FR Doc. 98-30332 Filed 11-12-98; 8:45 am]
BILLING CODE 4910-13-P
