AD 2001-20-02

[Federal Register Volume 66, Number 190 (Monday, October 1, 2001)]
[Rules and Regulations]
[Pages 49825-49827]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 01-24273]



[[Page 49825]]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 2000-NE-25-AD; Amendment 39-12448; AD 2001-20-02]
RIN 2120-AA64


Airworthiness Directives; Pratt & Whitney PW4000 Series Turbofan 
Engines

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment adopts a new airworthiness directive (AD), that 
is applicable to Pratt & Whitney (PW) PW4000 series turbofan engines 
with 2nd stage high pressure turbine (HPT) air seal assembly part 
number (P/N) 50L976 or P/N 50L960 installed. This amendment requires 
operators to recalculate 2nd stage HPT air seal assembly cycles-in-
service, based on flight hour-to-cycle ratio usage. This amendment also 
requires upon recalculation, initial and repetitive on-wing borescope 
inspections of 2nd stage HPT air seal assemblies for cracks based on 
the newly calculated service life. This amendment also requires the 
removal from service of any cracked seal assemblies, and the removal of 
seal assemblies at or before newly calculated service life limits. This 
amendment is prompted by reports that thirteen 2nd stage HPT air seal 
assemblies have been found cracked in the rim area. Although these 
thirteen air seals were operating in the hottest configuration design, 
which is no longer in service, the current design 2nd stage HPT air 
seal assemblies are still operating in a temperature environment that 
is hotter than anticipated. The actions specified by this AD are 
intended to prevent 2nd stage HPT air seal assembly fracture that could 
result in an uncontained engine failure.

DATES: Effective date November 5, 2001. The incorporation by reference 
of certain publications listed in the regulations is approved by the 
Director of the Federal Register as of November 5, 2001.

ADDRESSES: The service information referenced in this AD may be 
obtained from Pratt & Whitney, 400 Main Street, East Hartford, CT 
06108. 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.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal 
Aviation Regulations (14 CFR part 39) to include an AD that is 
applicable to PW PW4000 series turbofan engines with 2nd stage HPT air 
seal assembly P/N 50L976 or P/N 50L960 installed was published in the 
Federal Register on December 27, 2000 (65 FR 81780). That action 
proposed to require operators to recalculate 2nd stage HPT air seal 
assembly cycles-in-service, based on flight hour-to-cycle ratio usage. 
That action also proposed to require upon recalculation, initial and 
repetitive on-wing borescope inspections of 2nd stage HPT air seal 
assemblies for cracks based on the newly calculated service life, in 
accordance with PW ASB No. PW4G-112-A72-233, dated August 25, 2000. 
Finally, that action proposed to require removal from service of any 
cracked seal assemblies, and the removal of seal assemblies at or 
before newly calculated service life limits.

Comments

    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the comments received.

Reference to Service Bulletin Revisions

    One commenter requests that the AD reference Revision 1 of PW ASB 
PW4G-112-A72-233, dated January 18, 2001. That revision clarifies the 
procedures for mixed operation of ``long mission'' and ``short 
mission'' operation, and does not change the inspection requirements. 
The FAA agrees that Revision 1 of the ASB provides necessary 
clarification. However, since the publication of the NPRM, the 
manufacturer published several revisions to ASB PW4G-112-A72-233. The 
original issue of the ASB required a one-time borescope inspection for 
engines converted by SB PW4G-112-75-30 at the time of conversion. 
Revision 1, dated January 16, 2001, clarified mixed mission 
instructions and in-shop inspections. Revision 2, dated March 27, 2001, 
added a statement that if the conversion occurred before the 
requirement for the one-time inspection, the one-time inspection is 
performed within 250 cycles of the issue date of Revision 2. Revision 
3, dated August 3, 2001, removes all reference to a one-time 
inspection. These revisions do not change the inspection requirements 
referenced by the AD. Therefore, the SB reference has been changed in 
the AD to PW ASB PW4G-112-A72-233, Revision 3. However, inspections 
done in accordance with the original SB or any of the revisions are 
considered to be in compliance with the AD.

Mixed Cycle Operator's Instructions

    Two commenters request confirmation that for the Mixed-Cycle 
Operator's Instructions of the SB referenced by the NPRM, the hour-to-
cycle ratio does not need to be calculated prior to August 25, 2000, 
the original publication date of the ASB. The commenters request 
confirmation that the monthly hour-to-cycle ratio monitoring is 
required only after the initial hour-to-cycle ratio is calculated.
    The FAA agrees that there appears to be some ambiguity regarding 
when calculations for hour-to-cycle ratio must be performed in order to 
determine the initial inspection threshold. The ASB states that the 
determination of the total number of hours and cycles a 2nd stage air 
seal has accumulated is done ``up to this point.'' This means the 
calculation of the total number of cycles on the seals must be done in 
accordance with the SB for every month that the seal has been in 
service. Because the AD incorporates the instructions of the ASB by 
reference, the AD requires the calculation of equivalent cycles by the 
equation in paragraph 1. A. of the Mixed Cycle Operator's Instructions 
of the ASB on all the cycles that the seal has accumulated in service 
on the date that the calculation is performed. Paragraph (a) of the AD 
specifies that the initial inspection threshold must be determined 
within 30 days of the effective date of the AD. The wording of the AD 
does not need to be changed because the compliance is ``required as 
indicated, unless accomplished previously.'' If an operator made the 
determination of the initial inspection threshold utilizing the August 
25, 2000 date, prior to the publication of this AD, this would be in 
compliance with the AD. The FAA agrees that the monthly hour-to-cycle 
ratio monitoring is required only after the initial hour-to-cycle ratio 
is calculated.

Air Seal Inspection in the Shop

    One commenter requests clarification as to whether the ASB 
requirement for air seal inspection in the shop is included in the AD. 
The in-shop inspection requirements are not included in the AD. The 
NPRM

[[Page 49826]]

references the ``On-Wing'' inspection procedures of the ASB because the 
FAA determined by evaluation of risk assessment data that, at a 
minimum, the on-wing inspections are required to address the unsafe 
condition.

Applicable Engine Models

    One commenter notes that Pratt & Whitney SB PW4G-112-A72-233, 
referenced in the NPRM, does not list PW4074D, and PW4090-3 as 
applicable engine models. However, the Boeing master change for B777 
allows installation of these engine models. The commenter believes this 
AD and the SB should reflect the PW4074D and the PW4090-3 as applicable 
engine models. The FAA agrees. The Appliciability now reflects the 
PW4000 112 inch diameter series engine models: PW4074, PW4077, PW4077D, 
PW4084, PW4084D, PW4090, PW4090-3, PW4074D, PW4090D, PW4098.

AD Requirements for Converted Engines

    One commenter requests clarification of the AD requirements for 
engines that have been converted from Population 3 to Population 4 or 
from 90K-A to 90K-B prior to the initial inspection threshold. The AD 
does not require the one-time post-conversion inspection for engines 
that were converted per SB PW4G-112-75-30 or Special Instruction 134F-
98 to population 4 or population 90K-B prior to the installed air seal 
accruing 1,500 cycles for ``long mission'' operators or 3,300 cycles 
for ``short mission'' operators.

Alternative Inspection Procedure

    One commenter notes that the On-Wing inspection procedure described 
in the Accomplishment Instructions of PW ASB PW4G-112-A72-233 allows 
operators to follow Boeing AMM Chapter/Section 72-52-00 as an 
alternative. The commenter believes the AD should also allow operators 
to use the procedure in the Boeing AMM Chapter/Section 72-52-00. The 
FAA does not agree. The FAA has not reviewed and approved the Boeing 
AMM Chapter/Section 72-52-00 that is cross-referenced in the ASB. 
Therefore, the Boeing AMM is not incorporated by reference in this AD.

250 Flight Cycle Inspection Frequency

    One commenter requests that the exception provided by PW ASB PW4G-
112-A72-233 that allows operators to inspect every 250 cycles rather 
than track hour-to-cycle ratio be permitted in the AD. The commenter 
asks if the monthly hour-to-cycle ratio should be calculated from the 
first day to the last day of each month, or twelve nearly equally 
spaced increments in a given year. The FAA agrees. The 250 flight cycle 
inspection frequency, and a cycle limit of 8,000 cycles is a more 
conservative approach. The FAA agrees that this option should be 
allowed in the AD. In addition, the FAA agrees that twelve nearly 
equally spaced increments in a given year satisfies the intent of the 
term ``monthly.''

Complicated Control Mechanism

    One commenter expresses concern that the control mechanism 
established in the ASB and AD is too complicated for an operator to 
manage. The commenter believes that this kind of complication can cause 
human error, which can result in non-compliance to the ASB. The FAA 
disagrees that this AD establishes a control mechanism that is too 
complicated for an operator to manage and is prone to human error. 
While human error can be introduced into any process, this is unlikely 
to occur when diligence in process management is afforded to issues 
that are subject to regulatory action.

Clarification of Discussion Statements Requested

    One commenter requests a clarification of statements made in the 
Discussion section of the NPRM. The first sentence in the Discussion 
states, ``This proposal is prompted by reports that thirteen 2nd stage 
HPT air seal assemblies have been cracked in the rim area.'' The 
commenter requests that for clarification the following be added: 
``These thirteen air seals were operating in the hottest configuration 
design, which is no longer in service.'' The subsequent sentence would 
then say: ``However, the current design 2nd stage HPT air seal 
assemblies are still operating in a temperature environment that is 
hotter than the manufacturer anticipated.'' The FAA agrees and this 
clarification has been added to the summary section of this amendment.

Replacement Cost Inaccuracy

    One commenter notes an inaccuracy in the replacement cost used in 
the Economic Analysis. The cost of a new 2nd stage HPT air seal noted 
in the ASB is $213,990, whereas the cost stated in the NPRM is 
$235,950. The FAA agrees. Utilizing the $213,990 figure would decrease 
the overall estimated cost impact from $10,659,312 to $8,551,152, a 
reduction of $2,108,160.
    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.

Economic Analysis

    There are approximately 233 Pratt & Whitney (PW) PW4000 series 
turbofan engines with 2nd stage high pressure turbine (HPT) air seal 
assembly part number (P/N) 50L976 or P/N 50L960 installed in the 
worldwide fleet. The FAA estimates that 96 engines installed on 
airplanes of U.S. registry will be affected by this AD. The FAA also 
estimates that it would take approximately 2.3 work hours per engine to 
accomplish the proposed on-wing borescope inspection, and that the 
average labor rate is $60 per work hour. The FAA estimates that 
approximately 47% of the certified life of the affected parts will be 
lost. Required parts would cost $213,990 per engine. Based on these 
figures, the total cost impact of the proposed AD on U.S. operators is 
estimated to be $8,551,152.

Regulatory Impact

    This final rule does not have federalism implications, as defined 
in Executive Order 13132, because it would not have a substantial 
direct effect 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. Accordingly, 
the FAA has not consulted with state authorities prior to publication 
of this final rule.
    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 the DOT Regulatory Policies and 
Procedures (44 FR 11034, February 26, 1979); and (3) if promulgated, 
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 by contacting 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

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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 adding a new airworthiness directive to 
read as follows:

2001-20-02  Pratt & Whitney: Amendment 39-12448. Docket 2000-NE-25-
AD.

Applicability

    This airworthiness directive (AD) is applicable to Pratt & 
Whitney (PW): PW4074, PW4077, PW4077D, PW4084, PW4084D, PW4090, 
PW4090-3, PW4074D, PW4090D, and PW4098 turbofan engines with 2nd 
stage high pressure turbine (HPT) air seal assembly part number (P/
N) 50L976 or P/N 50L960 installed. These engines are installed on 
but not limited to Boeing 777 series airplanes.

    Note 1: This 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 (d) 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

    Compliance with this AD is required as indicated, unless already 
done.
    To prevent 2nd stage HPT air seal assembly failure that could 
result in uncontained engine failure, accomplish the following:

Calculation of Service Limits

    (a) Within 30 days of the effective date of this AD, and then 
each calendar month thereafter, determine the hour-to-cycle ratio of 
2nd stage HPT air seal assemblies based on the hours and cycles 
accumulated in the previous month in accordance with Paragraph 1 of 
the Accomplishment Instructions for air seal management of PW Alert 
Service Bulletin (ASB) No. PW4G-112-A72-233, Revision 3, dated 
August 3, 2001.The original ASB or any of the revisions may also be 
used and are considered to be in compliance with the AD.

Borescope Inspections

    (b) For 2nd stage HPT air seal assemblies, determine the initial 
inspection time and repetitive inspection interval in cycles, in 
accordance with Paragraph 2 of the Accomplishment Instructions for 
air seal management of PW ASB No. PW4G-112-A72-233; Revision 3, 
dated August 3, 2001. Perform borescope inspections of the 2nd stage 
HPT air seal assembly for cracks, and remove HPT air seal assemblies 
from service if cracked, in accordance with the On-Wing Procedure 
section of Accomplishment Instructions of PW ASB No. PW4G-112-A72-
233, Revision 3, dated August 3, 2001. Inspections done in 
accordance with the original ASB or any of the revisions are 
considered to be in compliance with the AD.

New Cycle Limits

    (c) Determine new cycle limits for 2nd stage HPT air seal 
assemblies in accordance with Paragraph 3 of the Accomplishment 
Instructions for air seal management of PW ASB No. PW4G-112-A72-233; 
Revision 3, dated August 3, 2001, and remove from service 2nd stage 
HPT air seal assemblies prior to exceeding those limits. 
Determinations made using the original ASB or any of the revisions 
are considered to be in compliance with the AD.

Alternative Methods of Compliance

    (d) 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 (ECO). 
Operators must submit their request through an appropriate Federal 
Aviation Administration (FAA) Principal Maintenance Inspector, who 
may add comments and then send it to the Manager, ECO.

    Note 2: Information concerning the existence of approved 
alternative methods of compliance with this airworthiness directive, 
if any, may be obtained from the ECO.

Special Flight Permits

    (e) Special flight permits may be issued in accordance with 
Secs. 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 
21.197 and 21.199) to operate the airplane to a location where the 
requirements of this AD can be accomplished.

Documents That Have Been Incorporated by Reference

    (f) The inspections must be done in accordance Pratt & Whitney 
ASB PW4G-112A72-233, Revision 3, dated August 3, 2001. 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 Street, 
East Hartford, CT 06108. 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.

Effective Date of This AD

    (g) This amendment becomes effective on November 5, 2001.

    Issued in Burlington, Massachusetts, on September 21, 2001.
Jay J. Pardee,
Manager, Engine and Propeller Directorate, Aircraft Certification 
Service.
[FR Doc. 01-24273 Filed 9-28-01; 8:45 am]
BILLING CODE 4910-13-P