Federal Register, Volume 74, Number 91, May 13, 2009, Pages 22417-22636 Page: 22,427
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Federal Register / Vol. 74, No. 91/Wednesday, May 13, 2009 / Rules and Regulations
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 ofif 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 tothe inspection. Delta Air Lines also asks
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 theHPT 2nd stage blade root serrations was
22427
establish a compliance schedule.
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United States. Office of the Federal Register. Federal Register, Volume 74, Number 91, May 13, 2009, Pages 22417-22636, periodical, May 13, 2009; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc132953/m1/18/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.