[Federal Register Volume 86, Number 142 (Wednesday, July 28, 2021)]
[Rules and Regulations]
[Pages 40299-40306]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2021-15947]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2020-0442; Project Identifier AD-2020-00260-E; 
Amendment 39-21640; AD 2021-14-13]
RIN 2120-AA64


Airworthiness Directives; Pratt & Whitney 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 all 
Pratt & Whitney (PW) PW2037, PW2037M, PW2040, and F117-PW-100 model 
turbofan engines. This AD was prompted by a report of an uncontained 
engine failure resulting from cracks in the knife edge of the high-
pressure turbine (HPT) 2nd-stage air seal assembly. This AD requires 
fluorescent penetrant inspections (FPIs) and visual inspections of the 
HPT 2nd-stage air seal assembly and, depending on the results of the 
inspections, replacement of the HPT 2nd-stage air seal assembly with a 
part eligible for installation. This AD also requires replacement of 
the affected HPT 2nd-stage air seal assembly, depending on the engine 
model, at either the next engine shop visit or the next piece-part 
opportunity. The FAA is issuing this AD to address the unsafe condition 
on these products.

DATES: This AD is effective September 1, 2021.

ADDRESSES: For service information identified in this final rule, 
contact Pratt & Whitney, 400 Main Street, East Hartford, CT 06118; 
phone: (800) 565-0140; fax: (860) 565-5442; email: [email protected]; 
website: https://fleetcare.pw.utc.com. You may view this service 
information at the FAA, Airworthiness Products Section, Operational 
Safety Branch, 1200 District Avenue, Burlington, MA 01803. For 
information on the availability of this material at the FAA, call (781) 
238-7759. It is also available at https://www.regulations.gov by 
searching for and locating Docket No. FAA-2020-0442.

Examining the AD Docket

    You may examine the AD docket at https://www.regulations.gov by 
searching for and locating Docket No. FAA-2020-0442; or in person at 
Docket Operations between 9 a.m. and 5 p.m., Monday through Friday, 
except Federal holidays. The AD docket contains this final rule, any 
comments received, and other information. The address for Docket 
Operations is U.S. Department of Transportation, Docket Operations, M-
30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue 
SE, Washington, DC 20590.

FOR FURTHER INFORMATION CONTACT: Carol Nguyen, Aviation Safety 
Engineer, ECO Branch, FAA, 1200 District Avenue, Burlington, MA 01803; 
phone: (781) 238-7655; fax: (781) 238-7199; email: 
[email protected].

SUPPLEMENTARY INFORMATION:

Background

    The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 
CFR part 39 by adding an AD that would apply to all PW PW2037, PW2037M, 
PW2040, and F117-PW-100 model turbofan engines. The NPRM published in 
the Federal Register on June 1, 2020 (85 FR 33043). The NPRM was 
prompted by a report of an uncontained engine failure resulting from 
cracks in the knife edge of the HPT 2nd-stage air seal assembly. After 
further analysis, it was determined that the knife-edge crack was due 
to seal rubbing that elevated the HPT 2nd-stage air seal assembly 
temperature and induced fatigue. In the NPRM, the FAA proposed to 
require initial and repetitive borescope inspections (BSIs), FPIs, and 
visual inspections of the HPT 2nd-stage air seal assembly and, 
depending on the results of the inspections, replacement of the HPT 
2nd-stage air seal assembly with a part eligible for installation. The 
NPRM also proposed to require replacement of the affected HPT 2nd-stage 
air seal assembly, depending on the engine model, at either the next 
engine shop visit or the next piece-part opportunity. The FAA is 
issuing this AD to address the unsafe condition on these products.

[[Page 40300]]

Discussion of Final Airworthiness Directive

Comments

    The FAA received comments from six commenters. The commenters were 
the Air Line Pilots Association, International (ALPA); Delta Air Lines, 
Inc. (Delta); FedEx Express (FedEx); MTU Maintenance Hannover GmbH 
(MTU); The Boeing Company (Boeing); and United Airlines (UAL).
    The following presents the comments received on the NPRM and the 
FAA's response to each comment.

Requests To Revise Proposed BSI Requirement

    Delta, MTU, and FedEx requested revisions to the BSI proposed in 
the NPRM. The FAA details the comments to the BSI in the following 
paragraphs but is not providing an individual response to each comment 
given that the FAA removed the proposal for BSI from this AD.

Request To Increase the Compliance Time for Initial BSI To Allow 
Sufficient Time To Complete Inspector Training

    Delta requested that the compliance time of 500 FCs after the 
effective date of this AD for the initial BSI proposed by paragraph 
(g)(1)(i) of the NPRM be extended to account for the difference in 
predicted flight utilization versus actual utilization as a result of 
the COVID-19 pandemic. Delta cited concerns that the 500 FC compliance 
time will not allow sufficient time for training inspectors to obtain 
qualifications to perform the BSI proposed by paragraph (g)(1)(i) of 
the NPRM. Delta noted that government restrictions and recommendations 
on travel and class size for in-person on-site training plus the lack 
of remote training opportunities represent obstacles to adequately 
training inspectors.

Request To Update Repetitive BSI Language

    Delta requested that the FAA update paragraph (g)(1)(ii) of the 
NPRM from ``. . . perform the BSI required by paragraph (g)(1)(i) of 
this AD within every 500 FCs since performance of the last BSI'' to ``. 
. . perform the BSI required by paragraph (g)(1)(i) of this AD within 
every 500 FCs since performance of the last BSI that was done per 
paragraph (g)(1)(i) or (g)(1)(ii) of this AD.'' Delta reasoned that the 
phrase ``last BSI'' of paragraph (g)(1)(ii) of the NPRM could cause 
confusion since the ``last BSI'' is the ``initial BSI.''

Request To Clarify ``Before Further Flight''

    Delta requested that the FAA update paragraph (g)(1)(iii) of the 
NPRM to clarify the phrase ``before further flight.'' Delta asked 
whether the action is to remove the engine before the flight of the 
aircraft, or remove the HPT 2nd-stage air seal assembly and perform the 
inspections proposed by paragraph (g)(2) of the NPRM before flight of 
the engine. Delta stated there could be confusion that the aircraft is 
prohibited from further flight until the HPT 2nd-stage air seal 
assembly is removed from the engine.

Request To Include a Scenario When To Perform the BSI

    Delta and MTU requested confirmation that the FAA included all the 
non-modulated turbine cooling air (TCA) system engines population into 
the proposed BSI requirement. MTU requested that the FAA update 
paragraph (g)(1) of the NPRM to include engines that have deactivated/
mechanically disconnected the TCA system.

Request To Update the Costs of Compliance and Work Hours

    FedEx requested that the hours to perform the BSI of the HPT 2nd-
stage air seal assembly be changed to 4.8 hours. FedEx cited PW Service 
Bulletin (SB) PW2000 72-773, dated March 11, 2020 (PW SB PW2000 72-
773), that indicates that the on-wing inspection takes 4.8 hours and 
not 2 work hours as indicated in the NPRM.

Request To Update the Terminating Action

    FedEx requested that the FAA revise paragraph (h), Terminating 
Action, of the NPRM from ``. . . terminating action for the repetitive 
BSI requirements in paragraph (g)(1)(ii) of this AD'' to ``. . . 
terminating action for the initial BSI requirement in paragraph 
(g)(1)(i) and the repetitive BSI requirements in paragraph (g)(1)(ii) 
of this AD.'' FedEx reasoned that an HPT 2nd-stage air seal assembly 
could be removed for a reason unrelated to this AD and inducted for an 
engine shop visit before the HPT 2nd-stage air seal assembly is subject 
to the initial BSI proposed by paragraph (g)(1)(i) of the NPRM. As 
written in the NPRM, FedEx suggested it could be interpreted that the 
HPT 2nd-stage air seal assembly would still need an initial inspection 
within 2,500 FCs after this unrelated engine shop visit.

Request To Clarify Revision of NDIP-1217

    Delta requested clarification if this AD allows for any revision 
level of Non-Destructive Inspection Procedure, Technique Sheet for 
Detection of Cracking in the PW2000 HPT 2nd Stage Airseal by Borescope 
Inspection Method (NDIP-1217). Delta cited paragraph (g)(1)(i) of the 
NPRM that proposed to require PW SB PW2000 72-773, which references 
NDIP-1217.

Request To Clarify Reporting

    Delta requested clarification if paragraph (g)(1)(i) of the NPRM 
proposed to require reporting of the inspection results to PW Materials 
& Processes Engineering/Non-Destructive Evaluation Engineer. Delta 
noted that paragraph (g)(1)(i) of the NPRM references paragraph 6 of PW 
SB PW2000 72-773, which references NDIP-1217, which specifies reporting 
of the inspection results.

Request To Approve Tooling Equivalent

    Delta requested that their rotator be approved as a tooling 
equivalent for performing the BSI proposed by paragraph (g)(1) of the 
NPRM. Delta reasoned that they worked in conjunction with PW to approve 
a tooling equivalent and requested confirmation that PW has the 
authority to approve tooling equivalents and that an alternative method 
of compliance request would not be required.
    Delta also requested approval to deviate from paragraph 6.1.2 of 
NDIP-1217 to remove the starter rather than the crank pad to use their 
rotator.

Request To Allow HPT Rotating by Hand for BSI

    Delta requested that the FAA allow the performance of the BSI of 
the HPT 2nd-stage air seal assembly proposed by paragraph (g)(1) of the 
NPRM to be rotated by hand rather than by a motor-driven unit per 
paragraph 6 of NDIP-1217. Delta reasoned the motor-driven unit may not 
be available at all stations and a second maintenance technician can 
rotate the HPT rotor manually, which allows the inspector to use two 
hands for the BSI.

Request To Confirm Affected Engine Serial Numbers

    Delta commented that ``EagleNet case (CAS-83493-C0M6W0)'' was 
submitted to P&W to confirm RTC engines cannot be converted to CET/pre-
CET engines or vice versa. Delta requested that the FAA confirm that 
the list of affected engine serial numbers in the proposed AD is an 
adequate method for controlling risk of affected population.

[[Page 40301]]

Comment on Operational and Economic Costs

    FedEx commented that the proposed rule would impact approximately 
half of its fleet of PW2000 model turbofan engines. The inspection 
program itself will have a minor operational impact as it can be 
incorporated into an existing hot section inspection program, but 
unplanned engine changes will result in local operational impact. FedEx 
noted that the cost of the on-wing inspection program [BSI] would be 
minimal but the cost of engines that need to be removed immediately 
will have a fairly significant impact. FedEx noted that these 
operational and economic impacts are acceptable when weighed against 
the impact of an in-service event.

FAA Response to Comments To Revise the BSI Inspection

    The FAA determined the need to remove the proposed BSI requirement 
from this AD based on comments regarding accessibility of inspector 
training. The FAA may consider additional rulemaking and will consider 
these comments in the development of any additional requirements.

Request That Individual Part Serviceability Not Depend on the 
Inspection Results of Other Parts

    Delta commented that individual part serviceability should not 
depend on the inspection results of other parts. Delta also commented 
that if inspections are not possible which would allow the mating HPT 
1st-stage disk or the HPT 2nd-stage hub to be deemed serviceable, 
independent from inspection status of the HPT 2nd-stage air seal 
assembly, then the manufacturer should revise the engine manuals to 
clarify that the mating HPT 1st-stage disk or HPT 2nd-stage hub cannot 
be made serviceable unless an inspection of the HPT 2nd-stage air seal 
assembly indicates it is free of cracks. Delta stated that this would 
remove the possibility that the mating HPT 1st-stage disk or HPT 2nd-
stage hub would be made serviceable and then installed in an engine 
before the HPT 2nd-stage air seal assembly is inspected.
    The FAA did not revise this AD in response to this comment. A 
crack, as identified in the shaded regions of Figure 1 to paragraph 
(g)(1)(iii) of this AD (Figure 1), which extends towards the knife-edge 
region of the HPT 2nd-stage air seal assembly, impacts the 
serviceability of the mating HPT 1st-stage disk and the HPT 2nd-stage 
hub. A crack identified in the shaded region of Figure 1 of this AD of 
the HPT 2nd-stage air seal assembly results in the requirement to 
remove the HPT 2nd-stage air seal assembly, mating HPT 1st-stage disk, 
and HPT 2nd-stage hub.

Request To Remove Inspections for Parts Being Scrapped

    Delta requested that the FAA update paragraph (g)(2)(i) of the NPRM 
(paragraph (g)(1)(i) of this AD) to remove the visual inspection, 
knife-edge coating strip, and FPI of the HPT 2nd-stage air seal 
assembly if the HPT 2nd-stage air seal assembly, mating HPT 1st-stage 
disk, and HPT 2nd-stage hub are being scrapped. Further, Delta 
requested if the HPT 2nd-stage air seal assembly is planned to be 
scrapped, then the mating HPT 1st-stage disk and HPT 2nd-stage hub be 
allowed to be made serviceable without FPI of the HPT 2nd-stage air 
seal assembly.
    The FAA disagrees with the need to change the AD based on this 
comment. If the HPT 2nd-stage air seal assembly, HPT 1st-stage disk, 
and HPT 2nd-stage hub are removed from service, then the inspections 
required by paragraph (g)(1)(i) of this AD are not applicable. The 
inspections are required only if the operator returns the parts to 
service.
    FPI is the only way to ensure the HPT 2nd-stage air seal assembly 
is free from cracks because an FPI will reveal cracks not detected by a 
visual inspection. The serviceability of the both the HPT 1st-stage 
disk and HPT 2nd-stage hub is directly dependent on the HPT 2nd-stage 
air seal assembly. If an operator does not FPI the HPT 2nd-stage air 
seal assembly, then neither the HPT 1st-stage disk nor HPT 2nd-stage 
disk can be returned to service. The FAA did not change this AD.

Request To Reference Engine Manual for Inspection Instructions

    FedEx requested that the FAA update paragraph (g)(2)(i) of the NPRM 
(paragraph (g)(1)(i) of this AD) to reference Chapter 72-52-60, 
Inspection/Check-01, of the PW2000 Series Engine Manual for 
instructions to perform the visual inspection, knife-edge coating 
removal, and FPI of the HPT 2nd-stage air seal assembly.
    The FAA determined it is not necessary to require use of specific 
service information as the visual inspection and FPI required by 
paragraph (g)(1)(i) of this AD are routine inspections that may vary 
between operators. The FAA, however, revised paragraph (g)(1)(i) of 
this AD to refer to Chapter 72-52-60, Repair-01, of the PW2000 Series 
Engine Manual for guidance on striping the knife edge coating from the 
HPT 2nd-stage air seal assembly.

Request To Remove FPI

    Delta requested that paragraph (g)(2)(ii) of the NPRM (paragraph 
(g)(1)(ii) of this AD) remove the proposed requirement to perform an 
FPI and require only visual inspections of the HPT 2nd-stage air seal 
assembly. Delta reasoned that based on NDIP-1217, cracks are detectable 
by visual inspection, thereby making FPI unnecessary. Delta concluded 
that performing only the visual inspection enables the HPT 2nd-stage 
air seal assembly to be inspected at initial disassembly while still in 
the presence of the mating HPT 1st-stage disk and HPT 2nd-stage hub, 
which simplifies determining if parts need to be scrapped if a crack is 
found. Otherwise, Delta stated that paragraph (g)(1)(iii) of the NPRM 
creates a logistical challenge for performing inspections as the HPT 
2nd-stage air seal assembly, mating HPT 1st-stage disk, and HPT 2nd-
stage hub could be routed to different locations with different lead 
times.
    The FAA disagrees. While cracks may be detected by visual 
inspection, an FPI will reveal cracks not detected by visual 
inspection. Additionally, the FPI is required to confirm that the HPT 
2nd-stage air seal assembly is free of cracks. The FAA did not change 
this AD.

Request To Allow Repair of the HPT 2nd-Stage Air Seal Assembly

    Delta and MTU requested that paragraph (g)(2)(ii) of the NPRM 
(paragraph (g)(1)(ii) of this AD) be updated to allow repair of the HPT 
2nd-stage air seal assembly if a crack is found. The commenters 
reasoned that Chapter 72-52-60, Inspection/Check-01 and Repair-02, of 
the PW2000 Series Engine Manual provides information for repairing a 
cracked HPT 2nd-stage air seal assembly. The commenters concluded that 
this AD should allow repair; otherwise, Chapter 72-52-60 of the PW2000 
Series Engine Manual should be deleted or updated.
    The FAA disagrees that the crack repairs identified in the engine 
manual should be incorporated in this AD. If a crack is found during 
the inspections required by this AD for the HPT 2nd-stage air seal 
assembly, the part must be removed from service and cannot be repaired. 
The FAA disagrees that Chapter 72-52-60 of the PW2000 Series Engine 
Manual should be deleted or updated. This repair is specifically for 
mechanical damage such as handling damage and foreign object damage in 
the knife edge area. This repair is not applicable to cracks identified 
by this AD. The damage addressed is unrelated and the repair does not 
need to be

[[Page 40302]]

prohibited. The requirements contained in this AD take precedence over 
any contrary provisions in the manufacturer's instructions for 
continued airworthiness. The FAA did not update this AD.

Request To Clarify Removal From Service

    Delta requested that the FAA clarify paragraph (g)(2)(ii) of the 
NPRM (paragraph (g)(1)(ii) of this AD) that states the HPT 2nd-stage 
air seal assembly must be removed from service if a crack is found. 
Delta asked if the HPT 2nd-stage air seal assembly must be scrapped, or 
if the HPT 2nd-stage air seal assembly can be repaired and returned to 
service after re-identifying it with a new P/N. Delta added that the 
engine manual provides a repair option of knife-edge cracks caused by 
mechanical damage.
    The FAA notes that ``remove from service'' in this AD indicates 
that the HPT 2nd-stage air seal assembly should be permanently removed 
from service if a crack is found. Any cracked HPT 2nd-stage air seal 
assembly cannot be repaired and returned to service per the 
requirements of this AD.

Request To Remove ``Before Further Flight''

    FedEx requested that the FAA remove the phrase ``before further 
flight'' from paragraphs (g)(2)(ii) and (iii) of the NPRM (paragraphs 
(g)(1)(ii) and (iii) of this AD). FedEx reasoned that since the visual 
inspection, knife edge coating removal, and FPI are performed at every 
piece-part opportunity of the mating HPT 1st-stage disk, HPT 2nd-stage 
disk, or the HPT 2nd-stage air seal assembly, ``before further flight'' 
is redundant. Additionally, FedEx stated that the overhaul facility 
must comply with the engine manual inspection criteria and would have 
no other option but to make the HPT 2nd-stage air seal assembly 
permanently unserviceable.
    The FAA agrees and removed ``before further flight'' from 
paragraphs (g)(1)(ii) and (iii) of this AD.

Request To Clarify Part Replacement After Crack Is Found

    MTU requested clarification regarding whether the mating HPT 1st-
stage disk or HPT 2nd-stage hub needs to be replaced if a crack is 
found after performing the inspections proposed by paragraph 
(g)(2)(iii) of the NPRM (paragraph (g)(1)(iii) of this AD), or if both 
the mating HPT 1st-stage disk and HPT 2nd-stage hub need to be 
replaced.
    If a crack is found as identified in the shaded region of Figure 1 
to paragraph (g)(1)(iii) of this AD (Figure 1) that extends toward the 
knife-edge region of the HPT 2nd-stage air seal assembly, this AD 
requires replacement of the HPT 2nd-stage air seal assembly, mating HPT 
1st-stage disk, and HPT 2nd-stage hub.

Request To Clarify Terminating Action

    UAL requested clarification if paragraph (h), Terminating Action, 
of the NPRM applies to the visual inspection and FPI of the HPT 2nd-
stage air seal assembly proposed by paragraph (g)(2) of the NPRM 
(paragraph (g)(1) of this AD).
    The FAA notes that there is no terminating action to the visual 
inspection and FPI of the HPT 2nd-stage air seal assembly required by 
paragraph (g)(1) of this AD. The visual inspection and FPI required by 
paragraph (g)(1) of this AD are required for all HPT 2nd-stage air seal 
assemblies, including P/Ns others than 1A8209 or 1A8209-001. As stated 
in an earlier response, with the removal of the BSI requirements from 
this AD, the FAA removed the terminating action from this AD.

Request To Clarify Applicability for Visual Inspection and FPI

    UAL requested clarification of whether paragraph (g)(1) of this AD 
applies if an HPT 2nd-stage air seal assembly, with a P/N other than P/
N 1A8209 or 1A8209-001, is installed.
    Delta requested that an applicability statement referencing P/Ns 
for affected HPT 2nd-stage air seal assemblies be added to paragraph 
(g)(2) of the NPRM. Paragraph (g)(2) of the NPRM proposed to require a 
visual inspection of the HPT 2nd-stage air seal assembly, stripping the 
knife edge coating from the HPT 2nd-stage air seal assembly, and then 
performing an FPI of the HPT 2nd-stage air seal assembly. Delta noted 
that if an HPT 2nd-stage air seal assembly has been modified and re-
identified with a new P/N using PW SB PW2000 72-754, Revision No. 2, 
dated April 30, 2019, then it should not be subject to the same 
inspections as HPT 2nd-stage air seal assembly, P/N 1A8209 or 1A8209-
001.
    The FAA disagrees and notes that the visual inspection and the FPI 
required by paragraph (g)(1)(i) of this AD are required for all HPT 
2nd-stage air seal assemblies, regardless of the P/N. The FAA did not 
update this AD.

Request To Allow Installation of Mating Parts Without Past HPT 2nd-
Stage Air Seal Assembly Inspection Verification

    Delta requested that a mating HPT 1st-stage disk and HPT 2nd-stage 
hub made serviceable before the effective date of this AD be eligible 
for installation without verification that all past HPT 2nd-stage air 
seal assemblies had visual inspections and FPI to verify no cracks were 
found. Delta reasoned that the inspections were not previously required 
and adequate records may not exist. Additionally, Delta stated it might 
not be possible to re-inspect all previous HPT 2nd-stage air seal 
assemblies for cracks as some may have been scrapped before the 
inspection.
    The FAA notes that an HPT 1st-stage disk and HPT 2nd-stage hub made 
serviceable before the effective date of this AD are not subject to the 
requirements of (g)(1)(iii) of the AD until their next piece part 
exposure. The FAA did not update this AD.

Request To Clarify the Location of the Forward and Aft Edges

    Delta and MTU requested that the FAA clarify the location of the 
forward and aft edges of the HPT 2nd-stage air seal assembly. Delta 
asked if the forward edge is the barrel section forward of the #1 
knife-edge or any part that extends beyond the barrel section.
    The FAA removed references to ``forward edge'' and ``aft edge'' of 
the HPT 2nd-stage air seal assembly from this AD. In their place, the 
FAA added Figure 1 to paragraph (g)(1)(iii) of this AD to specify the 
locations of the HPT 2nd-stage air seal assembly that require 
inspection for cracks.

Request To Clarify the Definition of Through-Crack

    Delta and FedEx requested that the FAA clarify the definition of 
``through-crack.'' Delta asked if a ``through-crack'' is a crack going 
through the axial direction or radial direction of the HPT 2nd-stage 
air seal assembly. Delta referenced Figure 5 of NDIP-1217 that appears 
to show a through-crack in the axial direction. Delta inferred from 
paragraph (i)(4) of the NPRM that a through-crack is in the radial 
direction. Delta requested a diagram to help illustrate what 
constitutes a through-crack.
    FedEx stated that a lenticular seal is a two-piece component that 
becomes an inseparable assembly during manufacturing. As a result, it 
would be impossible to distinguish a through-crack from a surface crack 
over a large area of the HPT 2nd-stage air seal assembly's exterior 
since its interior surfaces are inaccessible. FedEx cited Chapter 72-
52-60, Inspection/Check-01, Figures 801 and 801A, of the PW2000 Series 
Engine Manual, which highlights areas where through-thickness cracks 
are critical. According to FedEx, however, these images fail to address 
the ability to determine whether a surface crack is a ``through-
crack.'' Additionally, the PW2000 Series Engine

[[Page 40303]]

Manual does not provide dimensions that bound the areas making HPT disk 
replacement subjective.
    The FAA agrees that it is difficult to differentiate between a 
surface crack and through-crack; therefore, the FAA removed references 
to ``through-crack'' from this AD. The FAA notes that any crack, in any 
direction, found in the HPT 2nd-stage air seal assembly, requires 
removal of the HPT 2nd-stage air seal assembly from service. As stated 
in an earlier response, the FAA added Figure 1 to show the locations of 
the HPT 2nd-stage air seal assembly that require inspection for cracks. 
However, the FAA is not providing dimensions that bind the areas. If 
the inspections of the HPT 2nd-stage air seal assembly reveal a crack 
in the shaded regions of Figure 1, which extends towards the knife-edge 
region, the HPT 2nd-stage air seal assembly must be removed from 
service.

Request To Clarify Engine Shop Visit

    Delta requested that the FAA clarify the definition of ``engine 
shop visit'' related to which engine flanges the FAA considers ``major 
mating engine flanges.'' Delta requested that the FAA exclude the low-
pressure compressor (LPC) module flange as a major mating engine flange 
because LPC module life limited parts (LLPs) can be swapped while the 
engine is installed on the aircraft. Delta reasoned that the separation 
of the LPC module flange should not require replacement of the HPT 2nd-
stage air seal assembly. These LPC swaps may extend time between engine 
shop visits if the LLPs are located in the LPC.
    The FAA determined the need to revise the definition of ``engine 
shop visit'' by replacing separation of ``major mating engine flanges'' 
with separation of the ``N or M engine flange.'' If the LPC swap does 
not involve separating the N or M engine flange, then the compliance 
time for replacing the HPT 2nd-stage air seal assembly has not occurred 
as required by this AD.

Request To Update the Definition of Piece-Part Opportunity

    Delta requested that the FAA update the definition of ``piece-part 
opportunity'' from ``when the part is completely disassembled'' to 
``any time the seal is removed from the HPT module.'' Delta reasoned 
that while the HPT 2nd-stage air seal assembly is referred to as an 
``assembly,'' the HPT 2nd-stage air seal assembly cannot be dissembled.
    The FAA partially agrees and updated the definition to clarify what 
constitutes ``piece-part opportunity'' for the HPT 1st-stage disk, HPT 
2nd-stage hub, and HPT 2nd-stage air seal assembly.

Request To Update the Definition of Part Eligible for Installation

    Delta requested that the FAA update the definition of ``part 
eligible for installation'' to remove paragraph (i)(3)(ii) and to refer 
only to ``An HPT 2nd-stage air seal assembly that is not P/N 1A8209 or 
1A8209-001.'' Delta reasoned that paragraph (i)(3)(ii) of the NPRM, 
which states that an HPT 2nd-stage air seal assembly that has been 
modified using the service information is eligible for installation, is 
unnecessary because the HPT 2nd-stage air seal assembly receives a new 
P/N, which is not P/N 1A8209 or 1A8209-001, after repair.
    The FAA agrees and revised the definition of an HPT 2nd-stage air 
seal assembly that is eligible for installation, now in paragraph 
(h)(3) of this AD, to refer to an HPT 2nd-stage air seal assembly with 
a P/N other than 1A8209 or 1A8209-001.

Request To Update Service Information Revision

    MTU requested that the FAA reference PW SB PW2000 72-754, Revision 
No. 3, dated August 14, 2019, in this AD instead of Revision No. 2, 
dated April 30, 2019.
    The FAA agrees. The FAA updated PW SB PW2000 72-754 to Revision No. 
3, dated August 14, 2019, throughout this AD.

Request To Update the Service Information Description

    MTU requested that the FAA update the service information 
description in the Other Related Service Information paragraph of the 
NPRM (Related Service Information of this AD) to include the 
replacement and modification of the HPT 2nd-stage air seal assembly.
    The FAA agrees. The FAA updated the service information description 
in the Related Service Information paragraph in this AD.

Request To Update the Costs of Compliance

    UAL requested that the Costs of Compliance include additional costs 
such as delays in engine builds and modifications. UAL reasoned that 
piece-part modification of the HPT 2nd-stage air seal assembly, mating 
HPT 1st-stage disk, and HPT 2nd-stage hub are independent of each 
other. Scraping all parts proposed by paragraph (g)(2)(iii) of the NPRM 
(paragraph (g)(1)(iii) of this AD) will force engine centers to delay 
routing the mating HPT 1st-stage disk and HPT 2nd-stage hub for 
modification until the HPT 2nd-stage air seal assembly is inspected, 
thus delaying an engine build or incurring costs while the mating HPT 
1st-stage disk and HPT 2nd-stage hub are partially or fully scrapped.
    The FAA disagrees with updating the costs of compliance. The cost 
analysis in AD rulemaking actions typically includes only the costs 
associated with complying with the AD and does not include secondary 
costs. The FAA's cost estimate includes the work hours and parts costs 
to perform the required actions.

No Comments on This AD

    ALPA supported the AD and appreciated the opportunity to comment. 
Boeing had no comments.

Conclusion

    The FAA reviewed the relevant data, considered any comments 
received, and determined that air safety requires adopting this AD as 
proposed. Accordingly, the FAA is issuing this AD to address the unsafe 
condition on these products. Except for minor editorial changes, and 
any other changes described previously, this AD is adopted as proposed 
in the NPRM. None of the changes will increase the economic burden on 
any operator.

Related Service Information

    The FAA reviewed PW SB PW2000 72-754, Revision No. 3, dated August 
14, 2019, and PW SB PWF117 72-402, Revision No. 2, dated May 3, 2019. 
The SBs describe procedures for replacing or modifying the HPT 2nd-
stage air seal assembly.

Interim Action

    The FAA considers this AD to be an interim action. The FAA may 
consider additional rulemaking based on further investigation of the 
unsafe condition.

Costs of Compliance

    The FAA estimates that this AD affects 445 engines installed on 
airplanes of U.S. registry.
    The FAA estimates the following costs to comply with this AD:

[[Page 40304]]



                                                 Estimated Costs
----------------------------------------------------------------------------------------------------------------
                                                                                     Cost per      Cost on U.S.
                Action                         Labor cost           Parts cost        product        operators
----------------------------------------------------------------------------------------------------------------
Visually inspect, strip the knife edge  10 work-hours x $85 per               $0            $850        $378,250
 coating, and FPI the HPT 2nd-stage      hour = $850.
 air seal assembly.
----------------------------------------------------------------------------------------------------------------

    The FAA estimates the following costs to do any necessary 
replacements. The FAA has no way of determining how many replacements 
of the HPT 2nd-stage air seal assembly will be done with a modified HPT 
2nd-stage air seal assembly and how many will be done with a new HPT 
2nd-stage air seal assembly. The FAA also has no way of determining the 
number of engines that might need replacement of the HPT 2nd-stage air 
seal assembly, HPT 1st-stage disk, and HPT 2nd-stage hub.

                                               On-Condition Costs
----------------------------------------------------------------------------------------------------------------
                                                                                                     Cost per
                    Action                                 Labor cost               Parts cost        product
----------------------------------------------------------------------------------------------------------------
Replace the HPT 2nd-stage air seal assembly     10 work-hours x $85 per hour =            $5,000          $5,850
 with modified HPT 2nd-stage air seal assembly.  $850.
Replace the HPT 2nd-stage air seal assembly     0.25 work-hours x $85 per hour =         355,000      355,021.25
 with new seal assembly.                         $21.25.
Replace the HPT 2nd-stage air seal assembly,    0.25 work-hours x $85 per hour =         970,000      970,021.25
 HPT 1st-stage disk, and HPT 2nd-stage hub       $21.25.
 (based on FPI results).
----------------------------------------------------------------------------------------------------------------

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.
    The FAA is 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

    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) Will not affect intrastate aviation in Alaska, 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.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Incorporation by 
reference, Safety.

The Amendment

    Accordingly, under the authority delegated to me by the 
Administrator, the FAA 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:

2021-14-13 Pratt & Whitney: Amendment 39-21640; Docket No. FAA-2020-
0442; Project Identifier AD-2020-00260-E.

(a) Effective Date

    This airworthiness directive (AD) is effective September 1, 
2021.

(b) Affected ADs

    None.

(c) Applicability

    This AD applies to all Pratt & Whitney (PW) PW2037, PW2037M, 
PW2040, and F117-PW-100 model turbofan engines.

(d) Subject

    Joint Aircraft System Component (JASC) Code 7250, Turbine 
Section.

(e) Unsafe Condition

    This AD was prompted by a report of an uncontained engine 
failure resulting from cracks originating in the knife edge of the 
high-pressure turbine (HPT) 2nd-stage air seal assembly. The FAA is 
issuing this AD to prevent failure of the HPT 2nd-stage air seal 
assembly. The unsafe condition, if not addressed, could result in 
uncontained HPT 2nd-stage air seal assembly release, damage to the 
engine, and damage to the airplane.

(f) Compliance

    Comply with this AD within the compliance times specified, 
unless already done.

(g) Required Actions

(1) Visual Inspection and Fluorescent Penetrant Inspection (FPI) of 
HPT 2nd-Stage Air Seal Assembly

    After the effective date of this AD, at every piece-part 
opportunity of the HPT 1st-stage disk, HPT 2nd-stage hub, or the HPT 
2nd-stage air seal assembly:
    (i) Perform a visual inspection of the HPT 2nd-stage air seal 
assembly, strip the knife edge coating from the HPT 2nd-stage air 
seal assembly, and then perform an FPI of the HPT 2nd-stage air seal 
assembly.
    Note 1 to paragraph (g)(1)(i): Guidance on striping the knife 
edge coating from the HPT 2nd-stage air seal assembly required by 
paragraph (g)(1)(i) of this AD can be found Chapter 72-52-60, 
Repair-01, of the PW2000 Series Engine Manual.
    (ii) If a crack is found in the HPT 2nd-stage air seal assembly 
during the visual inspection or FPI required by paragraph (g)(1)(i) 
of this AD, remove the HPT 2nd-stage air seal assembly from service 
and replace it with a part eligible for installation.

[[Page 40305]]

    (iii) During the visual inspection or FPI required by paragraph 
(g)(1)(i) of this AD, if a crack is found in the shaded regions of 
the HPT 2nd-stage air seal assembly identified in Figure 1 to 
paragraph (g)(1)(iii) of this AD (Figure 1), which extends towards 
the knife-edge region of the HPT 2nd-stage air seal assembly, remove 
the HPT 2nd-stage air seal assembly, mating HPT 1st-stage disk, and 
HPT 2nd-stage hub from service, and replace the parts with parts 
eligible for installation. In order to return the mating HPT 1st-
stage disk and HPT 2nd-stage hub to service, the inspections of the 
HPT 2nd-stage air seal assembly cannot reveal a crack identified in 
the shaded regions of Figure 1, which extends towards the knife-edge 
region.
[GRAPHIC] [TIFF OMITTED] TR28JY21.013

(2) Replacement of HPT 2nd-Stage Air Seal Assembly

    (i) For PW PW2037, PW2037M, and PW2040 model turbofan engines, 
at the next engine shop visit after the effective date of this AD, 
remove the HPT 2nd-stage air seal assembly, part number (P/N) 1A8209 
or 1A8209-001, and replace it with a part eligible for installation.
    (ii) For PW F117-PW-100 model turbofan engines, at the next 
piece part opportunity after the effective date of this AD, remove 
the HPT 2nd-stage air seal assembly, P/N 1A8209 or 1A8209-001, and 
replace it with a part eligible for installation.

(h) Definitions

    (1) For the purpose of this AD, an ``engine shop visit'' is the 
induction of an engine into the shop for maintenance involving the 
separation of the N or M engine flange. The separation of engine 
flanges solely for the purposes of transportation of the engine 
without subsequent engine maintenance does not constitute an engine 
shop visit.
    (2) For the purpose of this AD, a ``piece-part opportunity'' is:
    (i) For the HPT 1st-stage disk, when the disk is removed from 
the engine and all the blades are removed;
    (ii) For the HPT 2nd-stage hub, when the hub is removed from the 
engine and all the blades are removed; or
    (iii) For the HPT 2nd-stage air seal assembly, when the assembly 
is removed from either the HPT 1st-stage disk or the HPT 2nd-stage 
hub.
    (3) For the purpose of this AD, a ``part eligible for 
installation'' is an HPT 2nd-stage air seal assembly with a P/N 
other than 1A8209 or 1A8209-001.

(i) Alternative Methods of Compliance (AMOCs)

    (1) The Manager, ECO Branch, FAA, has the authority to approve 
AMOCs for this AD, if requested using the procedures found in 14 CFR 
39.19. In accordance with 14 CFR 39.19, send your request to your 
principal inspector or local Flight Standards District Office, as 
appropriate. If sending information directly to the manager of the 
certification office, send it to the attention of the person 
identified in Related Information. You may email your request to: 
[email protected].
    (2) Before using any approved AMOC, notify your appropriate 
principal inspector, or lacking a principal inspector, the manager 
of the local flight standards district office/certificate holding 
district office.

[[Page 40306]]

(j) Related Information

    For more information about this AD, contact Carol Nguyen, 
Aviation Safety Engineer, ECO Branch, FAA, 1200 District Avenue, 
Burlington, MA 01803; phone: (781) 238-7655; fax: (781) 238-7199; 
email: [email protected].

(k) Material Incorporated by Reference

    None.

    Issued on June 30, 2021.
Ross Landes,
Deputy Director for Regulatory Operations, Compliance & Airworthiness 
Division, Aircraft Certification Service.
[FR Doc. 2021-15947 Filed 7-27-21; 8:45 am]
BILLING CODE 4910-13-P