[Federal Register: May 13, 2009 (Volume 74, Number 91)]
[Rules and Regulations]
[Page 22426-22429]
[DOCID:fr13my09-4]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2008-1131; Directorate Identifier 2008-NE-37-AD;
Amendment 39-15903; AD 2009-10-08]
RIN 2120-AA64

Airworthiness Directives; Pratt & Whitney Models PW2037,
PW2037(M), and PW2040 Turbofan Engines

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: The FAA is adopting a new airworthiness directive (AD) for
Pratt & Whitney models PW2037, PW2037(M), and PW2040 turbofan engines
with high-pressure turbine (HPT) 2nd stage hubs that have previously
been exposed to Pratt & Whitney cleaning procedure SPOP 10 or SPOP 9 or
equivalent procedure. This AD requires a onetime optical comparator
inspection (OCI) of the blade retention slots of the affected HPT 2nd
stage hubs at the next HPT overhaul after the effective date of the AD.
This AD results from an uncontained release of HPT 2nd stage blades and
blade retention lugs. We are issuing this AD to remove nonconforming
HPT 2nd stage hubs, which could result in an uncontained release of
turbine blades and blade retention lugs, and damage to the airplane.

DATES: This AD becomes effective June 17, 2009.

ADDRESSES: You can get the service information identified in this AD
from Pratt & Whitney, 400 Main Street, East Hartford, CT 06108.
    The Docket Operations office is located at Docket Management
Facility, U.S. Department of Transportation, 1200 New Jersey Avenue
SE., West Building Ground Floor, Room W12-140, Washington, DC 20590-
0001.

FOR FURTHER INFORMATION CONTACT: Mark Riley, Aerospace Engineer, Engine
Certification Office, FAA, Engine and Propeller Directorate, 12 New
England Executive Park, Burlington, MA 01803; e-mail:
<EMAIL_ADDRESS>telephone<PHONE_NUMBER>, fax<PHONE_NUMBER>.

SUPPLEMENTARY INFORMATION: The FAA proposed to amend 14 CFR part 39
with a proposed AD. The proposed AD applies to PW models PW2037,
PW2037(M), and PW2040 turbofan engines. We published the proposed AD in
the Federal Register on November 14, 2008 (73 FR 67427). That action
proposed to require inspecting all HPT 2nd stage hubs at the next HPT
overhaul after the effective date of the AD.

Examining the AD Docket

    You may examine the AD docket on the Internet at http://
www.regulations.gov; or in person at the Docket Operations office
between 9 a.m. and 5 p.m., Monday through Friday, except Federal
holidays. The AD docket contains this AD, the regulatory evaluation,
any comments received, and other information. The street address for
the Docket Operations office (telephone<PHONE_NUMBER>) is provided in
the ADDRESSES section. Comments will be available in the AD docket
shortly after receipt.

Comments

    We provided the public the opportunity to participate in the
development of this AD. We have considered the comments received.

Recommend Referring to the Inspection as ``Special Dimensional
Inspection''

    Pratt & Whitney recommends that the inspection in the proposed AD
be referred to as a ``Special Dimensional Inspection'' per Pratt &
Whitney Alert Service Bulletin (ASB) PW2000 72-734, which is approved
by the FAA. The proposed AD currently specifies an Optical Comparator
Inspection (OCI). Use of the term ``Special Dimensional Inspection''
instead of OCI will provide better alignment with the inspection
procedures that Pratt & Whitney is presently developing and for which
it will seek FAA approval, to use as an alternative to OCI.
    We do not agree. The inspection is an OCI. Therefore, identifying
the type of inspection the AD requires by its name is proper. We did
not change the AD.

Request To Revise the Estimated Cost

    Pratt & Whitney and two air carriers request that we revise the
estimated cost to perform an OCI. Pratt & Whitney states that the cost
is higher than previously anticipated and we should add about $4,000 to
the cost of each disk overhaul. Delta Air Lines states that the total
cost is actually closer to $8,000 and it should include shipping
($1,000), vendor charges ($5,900), and should take into account
additional inventory required ($180,000 per hub) due to out-of-service
time required to support the off-site inspection.
    We partially agree. We agree that the cost estimate in the proposed
AD is not accurate. We do not agree that it should consider shipping
charges or additional inventory requirements unique to each operator.
We changed the cost to perform the OCI to $4,000 for each HPT stage 2
hub as quoted by Pratt & Whitney and updated the total to $3,048,000.

Request for Clarification of the Inspection Being a Onetime Inspection

    Pratt & Whitney and two air carriers request clarification in the
AD to state that the inspection is a onetime inspection. Also, Delta
Air Lines comments that repetitive inspections should be required
unless the cause of the hub out-of-tolerance condition is addressed.
They also stated that the cause of the hub out-of-tolerance condition
is not known and repetitive inspections are therefore required.
    We partially agree. We agree that we need to clarify that the OCI
is a onetime inspection requirement. We changed the AD to clarify that
the OCI is a onetime inspection requirement. We do not agree that the
AD should require repetitive inspections. If we determine at a later
date that repetitive inspections are required, we may issue an AD to
require them.

Proposal To Eliminate the Fluorescent Penetrant Inspection

    Pratt & Whitney and United Airlines propose that we eliminate the
fluorescent penetrant inspection (FPI) requirement for the HPT 2nd
stage hub. FPI of the HPT 2nd stage hub is redundant, since it is
already mandated per FAA AD 2005-18-03.
    We agree. We changed the AD to only require a onetime OCI of the
HPT 2nd stage hub after the fluorescent penetrant

inspection and all shop cleaning processes have been completed.

Proposal To Reduce the Affected Population of HPT 2nd Stage Hubs

    Pratt & Whitney proposes that we reduce the affected population of
HPT 2nd stage hubs to only those that have been exposed to Pratt &
Whitney cleaning procedure SPOP 10 or SPOP 9 (cleaning processes that
have similar abrasive characteristics) during their shop overhaul
history. Based on recent findings from the NTSB-led investigation, the
blade slot dimensional variations on the event hub and on other
inspected hubs resulted from a specific process used during the
cleaning of hubs during the normal overhaul process.
    We agree. We changed the AD applicability to state that this AD
applies to Pratt & Whitney models PW2037, PW2037(M), and PW2040
turbofan engines with HPT 2nd stage hubs that have previously been
exposed to Pratt & Whitney cleaning procedure SPOP 10 or SPOP 9 or
equivalent procedure.

Proposal To Delay Issuance of AD

    United Airlines proposes that we delay issuance of the AD, because
initial OCI results are showing a 25% reject rate. This suggests that
the proposed inspections will not detect the problem that led to the
one industry failure. Otherwise, the industry failure rate would be
higher. Consequently, issuing the AD would be premature, as the failure
mechanism is not understood, and it is not clear that the proposed
inspections will prevent future failures.
    We do not agree. The investigation identified that an out-of-
tolerance condition of the HPT 2nd stage hub blade slots is the cause
of the failure event. However, the root cause of the out-of-tolerance
condition is still under investigation, but is believed to have been
caused by aggressive cleaning with an abrasive media blast. Inspection
of the HPT 2nd stage hub blade slots is required to identify hubs that
are out-of-tolerance, to minimize the risk of future failures. Pratt &
Whitney is reviewing the current acceptance criteria for the OCI of HPT
2nd stage hub blade slots, and if appropriate, may revise these limits
to reduce the current reject rate. We did not change the AD.

Proposal To Remove the Reporting Requirement From the AD

    Three air carriers propose that we remove the requirement for
operators to be responsible for reporting HPT 2nd stage hub OCI results
within 72 hours of the inspection. Delta Air Lines also asks if they
are required to report OCI results after the 6-month period, since not
all of their HPT 2nd stage hubs will go through overhaul within 6
months. The three air carriers state that it will be extremely
difficult for operators to comply with the reporting requirements of
the proposed rule, because it will not be the operators performing the
inspections. The sole source that performs the inspections, (Pratt &
Whitney), should be responsible for reporting to the FAA.
    We agree. We removed the reporting requirement from the AD.

Request That an Alternate Inspection Be Developed That Is Not Source-
Approved

    Two air carriers request that an alternate inspection method be
developed that is not source-approved and will permit all overhaul
shops the capability to perform the inspection. They state that Pratt &
Whitney is currently the only source-approved vendor for the OCI.
Operators are experiencing turn times in excess of 30 days, which is a
hardship to them.
    We agree that an alternate inspection procedure that can be
performed by all overhaul facilities is preferred. However, we are
unaware of any that may exist. We will evaluate any proposed
alternative inspection an operator may submit as an alternative method
of compliance. We did not change the AD.

Compliance Time Should Be Revised

    The National Transportation Safety Board (NTSB), states that the
compliance time should be revised to reflect the recommended compliance
time in the NTSB Urgent Safety Recommendation A-08-85. That compliance
time requires removal of all PW2037 2nd stage turbine hubs for
inspection when they have accumulated significantly fewer hours and/or
cycles than the incident engine (10,880 hours and/or 4,392 cycles). The
10,880 hours and 4,392 cycles referenced in A-08-85 were based on the
time and cycles that the incident engine had accumulated from the last
overhaul until engine failure. Metallurgical examination of the failed
hub was not able to discern any fatigue striations, so it is unknown
how long it took those fatigue cracks to progress to failure.
Typically, when the cause of the failure, or length of time for a crack
to progress to failure is unknown, the time and/or cycles, whichever is
less, since the part was new or overhauled until failure, is divided by
a factor of two or three to establish a compliance schedule.
    We do not agree. The field management plan defined in the proposed
AD is based on a risk analysis performed by Pratt &Whitney, which we
reviewed and concluded is adequate. Further, additional field data
received to-date has not indicated any increased risk, or that a more
restrictive field plan is required. We did not change the AD.

Proposed OCI Procedure Should Be Revised

    The NTSB states that the proposed OCI procedure should be revised
to also require that the blade slots be measured using a coordinate
measuring machine (CMM) or another dimensional inspection device
capable of measuring deviations in the center of the blade slots. The
OCI procedure is limited to only measure the blade slot profile on the
forward and aft ends of the blade slot. The current procedure does not
measure the center portion of the blade slot.
    We partially agree. We agree that the current OCI procedure is
limited such that it cannot measure the center portion of the blade
slot. However, we disagree that the OCI procedure is not an acceptable
inspection method to identify non-conforming hubs. We verified that the
OCI procedure can identify HPT 2nd stage hubs with non-conforming blade
retention slots. We established limits for OCI that ensured that no
parts with non-conformances similar to the event hub would be released
into service. We continue to work with Pratt & Whitney to identify
other improved inspection methods that can be used as an alternate to
OCI. We did not change the AD.

AD Compliance Should Also Include Inspection of the HPT 2nd Stage Blade
Root Serrations for Uneven Contact Wear

    The NTSB states that the AD compliance should also include
inspection of the HPT 2nd stage blade root serrations for uneven
contact wear, as defined in the PW2000 Engine Manual, Task 72-52-17-
200-014, Inspection/Check 14. The AD should also specify an action to
take with the HPT 2nd stage hubs if any HPT 2nd stage blades are
detected with uneven wear. The HPT 2nd stage blades removed from the
incident engine showed evidence of uneven contact wear on the blade
root serrations. The AD should therefore also include inspection of the
HPT 2nd stage blades and include an action to take with the hub if
blades are detected to have root serrations with uneven wear.
    We do not agree. Inspection of the HPT 2nd stage blade root
serrations was

incorporated in the PW2000 Engine Manual to address a non-conformance
issue for the blades and is performed during normal inspection. All
blades that are identified with uneven wear on the root serrations are
rejected and removed from service. The cause of failure of the incident
engine was due to a nonconformance of the HPT 2nd stage hub blade
retention slots. All HPT 2nd stage hubs that have previously been
exposed to Pratt & Whitney cleaning procedure SPOP 10 or SPOP 9 or
equivalent procedure will require OCI per the AD. All non-conforming
hubs will be identified by OCI and removed from service. We did not
change the AD.

AD Should Mandate That All of the HPT 2nd Stage Hub Blade Slots Be
Inspected Using OCI

    The NTSB states that the AD should mandate that all of the HPT 2nd
stage hub blade slots be inspected using OCI. The current procedure
only requires that every fourth blade retaining slot in the hub be
inspected. The incident engine had cracks in several adjacent blade
retaining lugs that resulted in the simultaneous release of multiple
blades that exceeded the turbine case's containment capability. If only
every fourth slot in the hub is inspected, then two adjacent
nonconforming blade slots could slip through the inspection and result
in an uncontained engine failure.
    We do not agree. Inspecting every fourth blade retaining slot will
identify all non-conforming hubs. HPT 2nd stage hubs that are
aggressively cleaned using a grit blast procedure will typically have a
high number of non-conforming slots. Field inspection data to-date
indicates that this assumption currently remains valid. We did not
change the AD.

Conclusion

    We have carefully reviewed the available data, including the
comments received, and determined that air safety and the public
interest require adopting the AD with the changes described previously.
We have determined that these changes will neither increase the
economic burden on any operator nor increase the scope of the AD.

Costs of Compliance

    We estimate that this AD will affect 762 engines installed on
airplanes of U.S. registry. We also estimate that it will take about 50
work-hours per engine to perform the actions, and that the average
labor rate is $80 per work-hour. No parts are required. Based on these
figures, we estimate the total cost of the AD to U.S. operators to be
$3,048,000.

Authority for This Rulemaking

    Title 49 of the United States Code specifies the FAA's authority to
issue rules on aviation safety. Subtitle I, Section 106, describes the
authority of the FAA Administrator. Subtitle VII, Aviation Programs,
describes in more detail the scope of the Agency's authority.
    We are issuing this rulemaking under the authority described in
Subtitle VII, Part A, Subpart III, Section 44701, ``General
requirements.'' Under that section, Congress charges the FAA with
promoting safe flight of civil aircraft in air commerce by prescribing
regulations for practices, methods, and procedures the Administrator
finds necessary for safety in air commerce. This regulation is within
the scope of that authority because it addresses an unsafe condition
that is likely to exist or develop on products identified in this
rulemaking action.

Regulatory Findings

    We have determined that this AD will not have federalism
implications under Executive Order 13132. This AD will 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.
    For the reasons discussed above, I certify that this AD:
    (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.
    We prepared a summary of the costs to comply with this AD and
placed it in the AD Docket. You may get a copy of this summary at the
address listed under ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

Adoption of the Amendment

0
Accordingly, under the authority delegated to me by the Administrator,
the Federal Aviation Administration amends 14 CFR part 39 as follows:

PART 39--AIRWORTHINESS DIRECTIVES

0
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]

0
2. The FAA amends Sec.  39.13 by adding the following new airworthiness
directive:

2009-10-08 Pratt & Whitney: Amendment 39-15903. Docket No. FAA-2008-
1131; Directorate Identifier 2008-NE-37-AD.

Effective Date

    (a) This airworthiness directive (AD) becomes effective June 17,
2009.

Affected ADs

    (b) None.

Applicability

    (c) This AD applies to Pratt & Whitney models PW2037, PW2037(M),
and PW2040 turbofan engines with high-pressure turbine (HPT) 2nd
stage hubs that have previously been exposed to Pratt & Whitney
cleaning procedure SPOP 10 or SPOP 9 or equivalent procedure. These
engines are installed on, but not limited to, Boeing 757-200 and
757-300 airplanes.

Unsafe Condition

    (d) This AD results from an uncontained release of HPT 2nd stage
blades and blade retention lugs. We are issuing this AD to remove
nonconforming HPT 2nd stage hubs, which could result in an
uncontained release of turbine blades and blade retention lugs, and
damage to the airplane.

Compliance

    (e) You are responsible for having the actions required by this
AD performed at the next HPT overhaul, unless the actions have
already been done.

Onetime Optical Comparator Inspection (OCI) of HPT 2nd Stage Hubs

    (f) Perform a onetime optical comparator inspection of the HPT
2nd stage hubs after a fluorescent penetrant inspection and all shop
cleaning processes have been completed. Pratt & Whitney Alert
Service Bulletin No. PW2000 A72-734, dated November 3, 2008,
contains information about the optical comparator inspection.
    (g) Remove from service any hubs that fail the optical
comparator inspection.

Definition

    (h) This AD defines an HPT overhaul as when the HPT is at its
piece-part level.

Alternative Methods of Compliance

    (i) The Manager, Engine Certification Office, has the authority
to approve alternative methods of compliance for this AD if
requested using the procedures found in 14 CFR 39.19.

Related Information

    (j) Contact Mark Riley, Aerospace Engineer, Engine Certification
Office, FAA, Engine and Propeller Directorate, 12 New England
Executive Park, Burlington, MA 01803; e-mail<EMAIL_ADDRESS>
telephone<PHONE_NUMBER>, fax<PHONE_NUMBER>, for more information
about this AD.
    (k) Pratt & Whitney Alert Service Bulletin No. PW2000 A72-734,
dated November 3, 2008, contains information about the optical
comparator inspection.

Material Incorporated by Reference

    (l) None.

    Issued in Burlington, Massachusetts, on May 4, 2009.
Peter A. White,
Assistant Manager, Engine and Propeller Directorate, Aircraft
Certification Service.
[FR Doc. E9-10953 Filed 5-12-09; 8:45 am]

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