Proposed Rules. Notice of proposed rulemaking (NPRM)

Agency: Federal Aviation Administration (FAA), DOT
Action: Notice of proposed rulemaking (NPRM)
Citation: FR Doc. 2026-05686 · RIN 2120-AA64 · Docket No. FAA-2026-2724; Project Identifier AD-2025-01606-E · 14 CFR 39

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.

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: Estimated Costs 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]