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 certain PW Model PW4074, PW4074D, PW4077, PW4077D, PW4084D, PW4090, and PW4090-3 engines. The NPRM was published in the Federal Register on June 6, 2025 (90 FR 24085). The NPRM was prompted by an analysis of an event involving an IAE LLC Model PW1127GA-JM engine, which experienced an HPC IBR-7 separation that resulted in an aborted takeoff. In the NPRM, the FAA proposed to require repetitive AUSIs of the HPC 15th-stage disks, front turbine hubs, HPT 1st-stage air seals, and HPT 2nd-stage hubs for crack indications, and removal from service and replacement if necessary. The FAA also proposed to require removal from service and replacement of the HPT 1st-stage air seal for certain serial numbers. The FAA is issuing this AD to address the unsafe condition on these products.

Discussion of Final Airworthiness Directive

Comments

The FAA received comments from six commenters. The commenters were the Air Line Pilots Association, International (ALPA), All Nippon Airways (ANA), The Boeing Company (Boeing), PW, United Airlines (United), and an individual. The following presents the comments received on the NPRM and the FAA's response to each comment.

Support for the NPRM

ALPA, Boeing, and United expressed support for the NPRM.

Request To Include “Or Later” Following Date of Material Citations

ANA requested that the FAA revise the material citations specified in paragraphs (g)(2)(i) through (iv) of the proposed AD to read “or later” following the revision date. ANA stated that if the material is revised in the future, an AMOC would be required for implementation.

The FAA disagrees with the request. To incorporate by reference (IBR) the material specified in this AD, the citation must refer to a specific document, including the specific revision date. Additionally, the FAA is unable to cite a future revision to a document which does not yet exist. If any of the specified material is revised, operators may request approval of an alternative method of compliance (AMOC) in accordance with the procedures in paragraph (j) of this AD. The FAA did not change this AD as a result of this comment.

Request To Clarify Revision Level for Secondary Material

ANA requested that the FAA revise the NPRM to include revision levels for certain non-destructive inspection procedures (NDIPs) which are referenced in the material specified in the NPRM, as well as paragraph (h) of the proposed AD; or refer to the service material instead. ANA stated that the material specifies instructions for performing AUSIs based on NDIPs, but the material does not specify a revision of the non-destructive inspection procedure for those actions. ( printed page 30192) Additionally, ANA indicated that maintenance, repair, and overhaul (MRO) organizations typically list compliance with service bulletins on the airworthiness release certificates, not compliance with NDIPs.

The FAA agrees to clarify. The IBR materials in this AD specify certain actions using certain NDIPs. All revisions of those specified NDIPs are acceptable for completing those actions. The FAA has not changed this AD based on this comment.

Request To Specify Certain Part Numbers in the Required Actions

ANA requested that the FAA include the affected part numbers in the required actions specified in paragraph (g)(2) of the proposed AD and throughout the NPRM. ANA stated that the NPRM requires certain actions for specified part nomenclature but does not include the relevant part numbers.

The FAA disagrees with the request. The nomenclature of the part is sufficient to identify the necessary actions. Additionally, the affected part numbers are specified in the IBR materials which are required to complete this AD. The FAA has not changed this AD based on this comment.

Request To Align Part Numbers with the Engine Illustrated Parts Catalog (EIPC)

ANA requested that the FAA change the part numbers for eligible parts in the NPRM to align with those provided in the EIPC. ANA stated that some of the part numbers listed as parts eligible for installation in the NPRM are not listed in the EIPC, and that ANA is unable to manage the required action without part numbers based on the EIPC.

The FAA disagrees with the request. The EIPC is intended to depict part and hardware relationships and accessibility for procurement. However, the EIPC does not define applicability for inspections or whether certain parts are eligible for installation. The part numbers specified in this AD are based on the manufacturer's service material and engineering analysis. Additionally, under the provisions of paragraph (j) of this AD, the FAA will consider requests for approval of an AMOC if sufficient data are submitted to substantiate an acceptable level of safety. The FAA has not changed this AD based on this comment.

Request To Shorten Compliance Times

An individual commenter requested that the FAA shorten the compliance times specified in the NPRM. The commenter stated that the current deadlines for compliance are too relaxed and do not match the urgent need to prevent dangerous failures in key engine parts. The commenter stated that the recent incident, where an HPC IBR-7 separation that resulted in an aborted takeoff, clearly shows how immediate this threat is. The commenter requested more immediate corrective measures with clear deadlines.

The FAA disagrees with the request. The commenter did not provide specific recommendations for alternative compliance times or justification for why the proposed compliance times are insufficient. In developing an appropriate compliance time, the FAA used a data-driven, quantitative risk analysis which considered the safety implications, parts availability, and normal maintenance schedules for timely accomplishment. In consideration of all these factors, the FAA selected the compliance times to appropriately mitigate the risk associated with the unsafe condition. This AD permits operators to accomplish the required actions at a time earlier than the specified compliance time. If additional data are presented that justify a shorter compliance time, the FAA may consider further rulemaking on this issue. The FAA did not change this AD as a result of this comment.

Request for Targeted Metallurgical Testing

An individual commenter requested that the FAA require targeted metallurgical testing on samples from specific production campaigns where variability is suspected. The commenter discussed the nature of nickel powder metallurgy; that minor variations can create microscopic defects, which may become weaknesses under stress; and that some production batches are already shown to have resultant anomalies, which reduce component fatigue life, especially in high-pressure compressors and turbines. The commenter stated that results from the focused testing could be used to confirm whether additional parts are at risk and allow the FAA to adjust inspection intervals accordingly.

The FAA disagrees with the request. The commenter did not provide any specific recommendations for changes to the actions required by this AD. The FAA has determined that the manufacturer has improved their manufacturing and inspection processes and has identified all at-risk part populations. Additionally, metallurgical testing of this kind is industry standard as part of the manufacturing quality control process. The FAA did not change this AD as a result of this comment.

Request To Broaden Scope of Affected Parts

An individual commenter requested that the FAA broaden the criteria for evaluation or establish a mechanism for rapid re-evaluation of affected parts in the NPRM. The commenter stated that focusing on specific serial numbers and part numbers is overly narrow, that the risk posed by nickel powdered metal inconsistencies is not confined solely to these items, and that production variability may affect a larger fraction of similar components. The commenter indicated that parts from adjacent production campaigns or exhibiting borderline metallurgical characteristics might equally be at risk. The commenter stated that broadening the scope of the criteria would ensure additional hazardous components are identified and managed, which would reduce the potential for at-risk parts to be overlooked.

The FAA disagrees with the request. The FAA has determined that there are no adjacent production campaigns and, as stated previously, the manufacturer has identified all at-risk part populations. Therefore, this AD applies to the part numbers and serial numbers of all at-risk components. The FAA did not change this AD as a result of this comment.

Request for Time-Based Inspection Intervals

An individual commenter requested that the FAA revise the NPRM to include uniform time-based inspection intervals. The commenter stated that reliance on “piece part opportunities” introduces significant variability into the safety assurance process. The commenter indicated that because each operator follows an independent maintenance schedule, some engines may continue operating with undetected degradation for extended periods, which could jeopardize the safety of the fleet.

The FAA disagrees with the request. The commenter did not provide specific recommendations for alternative time-based inspection intervals or justification for why the proposed compliance times are insufficient. The FAA acknowledges that piece-part opportunities can be variable. However, as discussed previously, in developing an appropriate compliance time, the FAA used a data-driven, quantitative risk analysis which considered the safety implications, parts availability, and normal maintenance schedules for timely accomplishment, which included both the variability and the worst-case ( printed page 30193) scenarios. This information was then used to determine that piece part opportunities appropriately mitigate the risk associated with the unsafe condition. If additional data are presented that justify a uniform time-based inspection interval, the FAA may consider further rulemaking on this issue. The FAA did not change this AD as a result of this comment.

Request for Mandatory Reporting

An individual requested that the FAA require mandatory reporting in the NPRM. The commenter stated that data from operators for parts with abnormal degradation, even without an in-flight failure, would offer insight into the condition of nickel powdered metal components and allow the FAA to identify trends early and prevent accidents.

The FAA disagrees with the request. This request falls outside the scope of this AD, whereas the intent is to detect nickel powder anomalies, related cracking, and replace the affected parts. The FAA has a clear understanding of the failure mode, and mandatory reporting would not increase knowledge of the unsafe condition. Additionally, these specific nickel powder components do not exhibit abnormal degradation. Failures or crack indications found during the inspections required by this AD are already subject to existing mandatory reporting requirements of the manufacturer. The FAA did not change this AD as a result of this comment.

Request for Data Sharing and Transparency

An individual commenter requested that the FAA publicly share aggregated inspection and test results. The commenter stated that the FAA should be prompt and transparent, and that making this data publicly available would empower the aviation community to understand the full scope of the unsafe condition and collaborate in development of best practices and corrective measures. The commenter referenced similar transparency measures within the automotive and rail industries, which improved identification of emerging safety issues and allowed more effective collaborative solutions. The commenter stated that this demonstrated clear benefits of open data sharing in enhancing overall safety.

The FAA disagrees with the request to share data. Much of the requested aggregated data is proprietary and, consequently, the FAA is unable to share publicly. As discussed previously, the FAA and the manufacturer have clear understanding of the failure mode and unsafe condition. The intent of this AD is to detect nickel powder anomalies and related cracking and replace the affected parts. The FAA, the manufacturer, the rest of the industry, and many industry groups have mechanisms in place to share information and develop industry best practices. The FAA did not change this AD as a result of this comment.

Request To Mandate Airworthiness Limitations Section (ALS) Updates Instead of Service Material

PW requested that the FAA revise the NPRM to require updating the ALS instead of the actions specified in the service material. PW stated that the inspections specified in the service material for the HPC 15th-stage disks, front turbine hubs, HPT 1st-stage air seals, and HPT 2nd-stage hubs have since been included in the revised engine manual ALS and are now duplicate requirements.

The FAA partially agrees with the request. The FAA disagrees with the request to require updating the ALS rather than performing certain inspections in accordance with the service material; however, the FAA finds that updating the engine manual ALS provides acceptable mitigation of the unsafe condition. The FAA has added paragraph (i) of this AD, which provides optional terminating action for operators that update their engine manual ALS to include the actions required by paragraphs (g)(1) through (3) of this AD.

Request To Eliminate the Requirement To Remove From Service

PW requested that the FAA eliminate paragraph (g)(3) of the proposed AD. PW stated that the requirement to remove the part from service is sufficiently covered by existing inspection procedures which are incorporated in the revised engine manual ALS inspections.

The FAA disagrees with the request. This AD does not require any engine manual ALS updates. Therefore, the FAA finds that including removal requirements in this airworthiness directive is both appropriate and necessary. However, as previously discussed, the FAA has added paragraph (i) of this AD which provides optional terminating action for operators that update their engine manual ALS to include the actions required by paragraphs (g)(1) through (3) of this AD. The FAA did not change this AD as a result of this comment.

Request To Remove Certain Definition of “Piece Part Opportunity”

PW requested that the FAA remove the definitions specified in paragraphs (h)(1)(i) through (iii) of the proposed AD. PW stated that “piece part opportunity” is already defined in the revised engine manual ALS inspections.

The FAA disagrees with the request. A definition for “piece part opportunity” is necessary for the required actions in this AD because the ALS update is an optional terminating action and not mandatory. The FAA did not change this AD as a result of this comment.

Request To Remove Certain Definition of “Part Eligible for Installation”

PW requested that the FAA remove the definitions specified in paragraph (h)(2) of the proposed AD. PW stated that “part eligible for installation” is already defined in the revised engine manual ALS inspections. PW proposed that the FAA allow all new manufactured parts to be eligible for installation regardless of confirmation of receiving an angle ultrasonic scan inspection (AUSI). PW indicated its fleet management plan does not require confirmation that new affected parts have received an AUSI during manufacture to be eligible for installation. PW stated that including such a requirement places an unnecessary burden on operators.

The FAA partially agrees with this request. The FAA disagrees with removing the definition of “Part Eligible for Installation” from this AD. However, the FAA agrees that operators do not have access to the necessary data to determine whether zero-time components have passed an AUSI at new part manufacture. Therefore, the FAA has determined that the responsible party may determine if the part is eligible for installation based on the date specified on the FAA Form 8130-3. The FAA has revised paragraphs (h)(2)(xiii) of this AD by removing the words “and has passed an AUSI at new part production” and replacing them with “that has an FAA Form 8130-3 from the original equipment manufacturer for new production dated July 1, 2025, or later.”

Explanation of Change to the Type Certificate Holder's Name

The FAA has revised the applicability of this AD to identify the type certificate holder's name as published in the most recent type certificate data sheet for the affected models. ( printed page 30194)

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.

Material Incorporated by Reference Under 1 CFR Part 51

The FAA reviewed the following material:

• PW Alert Service Bulletin (ASB) PW4G-112-A72-365, Revision No. 1, dated June 20, 2024, which specifies procedures for performing repetitive AUSIs on affected HPC 15th-stage disks.
• PW ASB PW4G-112-A72-366, dated June 20, 2024, which specifies procedures for performing repetitive AUSIs on affected HPT 1st-stage air seals.
• PW ASB PW4G-112-A72-367, dated June 20, 2024, which specifies procedures for performing repetitive AUSIs on affected front turbine hubs.
• PW ASB PW4G-112-A72-368, dated June 20, 2024, which specifies procedures for performing repetitive AUSIs on affected HPT 2nd-stage hubs.

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.

Costs of Compliance

The FAA estimates that this AD affects 124 engines installed on airplanes of U.S. registry. The FAA estimates that 124 engines will need AUSIs of the HPC 15th-stage disk, front turbine hub, HPT 2nd-stage hub, and HPT 1st-stage air seal; and 6 engines will need replacement of the HPT 1st-stage air seals.

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

The FAA estimates the following costs to do any replacements that would be required based on the results of the inspection. The agency has no way of determining the number of engines that might need these replacements:

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.

The Amendment

Accordingly, under the authority delegated to me by the Administrator, the FAA amends 14 CFR part 39 as follows: