FAA Proposed Airworthiness Directive for Pratt & Whitney Engines

Content

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

The FAA proposes to adopt a new airworthiness directive (AD) for certain Pratt & Whitney Division (PW) Model PW4074D, PW4077D,
PW4084D, PW4090, and PW4090-3 engines. This proposed AD was prompted by the discovery of a quality escape involving incorrect
shot peening on certain high-pressure compressor (HPC) drum rotor disk assemblies. This proposed AD would require visually
inspecting the HPC drum rotor disk assembly for incorrect shot peen coverage and,

     depending on the results of the inspection, replacing the HPC drum rotor disk assembly with a part eligible for installation.
     This proposed AD would also require removing and replacing certain HPC drum rotor disk assemblies before reaching certain
     life limits. The FAA is proposing this AD to address the unsafe condition on these products.

DATES:

The FAA must receive comments on this proposed AD by May 8, 2026.

ADDRESSES:

You may send comments, using the procedures found in 14 CFR 11.43 and 11.45, by any of the following methods:

• Federal eRulemaking Portal: Go to regulations.gov. Follow the instructions for submitting comments.

• Fax: (202) 493-2251.

• Mail: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue
SE, Washington, DC 20590.

• Hand Delivery: Deliver to Mail address above between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

AD Docket: You may examine the AD docket at regulations.gov under Docket No. FAA-2026-2724; 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 NPRM, any comments received, and other information. The street address for Docket
Operations is listed above.

Material Incorporated by Reference:

• PW material identified in this proposed AD, contact PW, 400 Main Street, East Hartford, CT 06118; phone: (800) 565-0140;
email: help24@prattwhitney.com; website: connect.prattwhitney.com.

• You may view this material 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 (817) 222-5110.

FOR FURTHER INFORMATION CONTACT:

Molly Sturgis, Aviation Safety Engineer, FAA, 2200 South 216th Street, Des Moines, WA 98198; phone: (562) 627-5373; email: molly.a.sturgis@faa.gov.

SUPPLEMENTARY INFORMATION:

Comments Invited

The FAA invites you to send any written relevant data, views, or arguments about this proposal. Send your comments using a
method listed under the
ADDRESSES
section. Include “Docket No. FAA-2026-2724; Project Identifier AD-2025-01606-E” at the beginning of your comments. The most
helpful comments reference a specific portion of the proposal, explain the reason for any recommended change, and include
supporting data. The FAA will consider all comments received by the closing date and may revise this proposal because of those
comments.

Except for Confidential Business Information (CBI) as described in the following paragraph, and other information as described
in 14 CFR 11.35, the FAA will post all comments received, without change, to regulations.gov, including any personal information you provide. The agency will also post a report summarizing each substantive verbal contact
received about this NPRM.

Confidential Business Information

CBI is commercial or financial information that is both customarily and actually treated as private by its owner. Under the
Freedom of Information Act (FOIA) (5 U.S.C. 552), CBI is exempt from public disclosure. If your comments responsive to this
NPRM contain commercial or financial information that is customarily treated as private, that you actually treat as private,
and that is relevant or responsive to this NPRM, it is important that you clearly designate the submitted comments as CBI.
Please mark each page of your submission containing CBI as “PROPIN.” The FAA will treat such marked submissions as confidential
under the FOIA, and they will not be placed in the public docket of this NPRM. Submissions containing CBI should be sent to
Molly Sturgis, Aviation Safety Engineer, FAA, 2200 South 216th Street, Des Moines, WA 98198. Any commentary that the FAA receives
which is not specifically designated as CBI will be placed in the public docket for this rulemaking.

Background

The FAA was notified by the manufacturer of a problem with PW Model PW4074D, PW4077D, PW4084D, PW4090, and PW4090-3 engines
where a repair shop quality escape revealed that certain HPC drum rotor disk assemblies were shot peened in an area where
peening was prohibited. Further investigation by the manufacturer revealed that incorrect shot peening of the HPC drum rotor
disk assembly reduces the life of the part, and PW identified a select number of fielded HPC drum rotor disk assemblies which
could have experienced the same quality escape and may have been peened in a prohibited area. As a result, PW revised the
airworthiness limitations section of the existing aircraft maintenance manual to reflect the reduced life limit for the affected
part and published updated service material with instructions for removal of affected HPC drum rotor disk assemblies prior
to reaching the updated reduced life limits, and inspections of affected HPC drum rotor disk assemblies for incorrect shot
peening. This condition, if not addressed, could result in uncontained debris release, damage to the engine, and damage to
the airplane.

FAA's Determination

The FAA is issuing this NPRM after determining that the unsafe condition described previously is likely to exist or develop
on other products of the same type design.

Material Incorporated by Reference Under 1 CFR Part 51

The FAA reviewed PW Alert Service Bulletin (ASB) PW4G-112-A72-373, Original Issue, dated September 10, 2025. This material
specifies procedures for a visual inspection of the HPC drum rotor disk assembly for incorrect shot peen coverage. This material
also provides updated inspection thresholds for visual inspection of affected HPC drum rotor disk assemblies. This material
is reasonably available because the interested parties have access to it through their normal course of business or by the
means identified in the
ADDRESSES
section.

Proposed AD Requirements in This NPRM

This proposed AD would require visually inspecting the HPC drum rotor disk assembly for incorrect shot peen coverage before
accumulating between 8,600 and 10,400 total life cycles since new, as applicable to HPC drum rotor disk assembly, and, depending
on the results of the inspection, replacing the HPC drum rotor disk assembly with a part eligible for installation. This proposed
AD would also require removing and replacing certain HPC drum rotor disk assemblies before reaching certain life limits.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would affect three engines installed on airplanes of U.S. registry.
The FAA estimates that there is one engine installed on airplanes of U.S. registry with an HPC drum rotor disk assembly installed
that require replacement of the HPC drum rotor disk assembly at the reduced life limit.

The FAA estimates the following costs to comply with this proposed AD:

| Action | Labor cost | Parts cost | Cost per
product | Cost on U.S. operators |
| --- | --- | --- | --- | --- |
| Visually inspect HPC drum rotor disk assembly | 10 work-hours × $85 per hour = $850 | $0 | $850 | $2,550. |
| Replace HPC drum rotor disk assembly | 10 work-hours × $85 per hour = $850 | 1,622,040 | 1,622,890 | Up to $6,491,560. |

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

The FAA determined that this proposed AD would not have federalism implications under Executive Order 13132. This proposed
AD 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.

For the reasons discussed above, I certify this proposed regulation:

(1) Is not a “significant regulatory action” under Executive Order 12866,

(2) Would not affect intrastate aviation in Alaska, and

(3) Would 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 Proposed Amendment

Accordingly, under the authority delegated to me by the Administrator, the FAA proposes to amend 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.

§ 39.13 [Amended] 2. The FAA amends § 39.13 by adding the following new airworthiness directive:

Pratt & Whitney Division:
Docket No. FAA-2026-2724; Project Identifier AD-2025-01606-E.

(a) Comments Due Date

The FAA must receive comments on this airworthiness directive (AD) by May 8, 2026.

(b) Affected ADs

None.

(c) Applicability

This AD applies to all Pratt & Whitney Division (PW) Model PW4074D, PW4077D, PW4084D, PW4090, and PW4090-3 engines.

(d) Subject

Joint Aircraft System Component (JASC) Code 7230, Turbine Engine Compressor Section.

(e) Unsafe Condition

This AD was prompted by the discovery of a quality escape involving incorrect shot peening on certain high-pressure compressor
(HPC) drum rotor disk assemblies. The FAA is issuing this AD to prevent failure of the HPC drum rotor disk assembly. The unsafe
condition, if not addressed, could result in uncontained debris 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) Definition

For the purpose of this AD, a “part eligible for installation” is any HPC drum rotor disk assembly having a part number (P/N)
and serial number (S/N) that is not identified in paragraph (h) of this AD.

(h) Required Actions

(1) For HPC drum rotor disk assemblies having P/N 50S634, and S/N CENCD26931, CENCD29577, CENCD29597, CENCD41851, or CENCD43536,
as applicable, before accumulating the total life cycles since new in Table 1 of the Accomplishment Instructions of PW Alert
Service Bulletin (ASB) PW4G-112-A72-373, Original Issue, dated September 10, 2025 (PW ASB PW4G-112-A72-373, Original Issue),
perform a visual inspection of the HPC drum rotor disk assembly in accordance with the Accomplishment Instructions, paragraph
1.B., of PW ASB PW4G-112-A72-373, Original Issue.

(2) If, during the inspection required by paragraph (h)(1) of this AD, evidence of incorrect shot peening is discovered, before
further flight, replace the HPC drum rotor disk assembly with a part eligible for installation.

(3) For the HPC drum rotor disk assembly having P/N 50S634 and S/N CENCD30975, before accumulating 9,800 total life cycles
since new, remove the HPC drum rotor disk assembly from service and replace with a part eligible for installation.

(4) For the HPC drum rotor disk assembly having P/N 50S634 and S/N CENCD42978, before accumulating 11,000 total life cycles
since new, remove the HPC drum rotor disk assembly from service and replace with a part eligible for installation.

(i) Alternative Methods of Compliance (AMOCs)

The Manager, AIR-520 Continued Operational Safety 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 AIR-520 Continued
Operational Safety Branch, send it to the attention of the person identified in paragraph (j) of this AD and email to: AMOC@faa.gov. 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.

(j) Additional Information

For more information about this AD, contact Molly Sturgis, Aviation Safety Engineer, FAA, 2200 South 216th Street, Des Moines,
WA 98198; phone: (562) 627-5373; email: molly.a.sturgis@faa.gov.

(k) Material Incorporated by Reference

(1) The Director of the Federal Register approved the incorporation by reference (IBR) of the material listed in this paragraph
under 5 U.S.C. 552(a) and 1 CFR part 51.

(2) You must use this material as applicable to do the actions required by this AD, unless the AD specifies otherwise.

(i) Pratt & Whitney Division (PW) Alert Service Bulletin PW4G-112-A72-373, Original Issue, dated September 10, 2025.

(ii) [Reserved]

(3) For PW material identified in this AD, contact PW, 400 Main Street, East Hartford, CT 06118; phone: (800) 565-0140; email: help24@prattwhitney.com; website: connect.prattwhitney.com.

(4) You may view this material 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 (817) 222-5110.

(5) You may view this material at the National Archives and Records Administration (NARA). For information on the availability
of this material at NARA, visit www.archives.gov/federal-register/cfr/ibr-locations or email fr.inspection@nara.gov.

Issued on March 20, 2026. Peter A. White, Deputy Director, Integrated Certificate Management Division, Aircraft Certification Service. [FR Doc. 2026-05686 Filed 3-23-26; 8:45 am] BILLING CODE 4910-13-P

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