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-2026-3875; Project Identifier AD-2025-01365-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 Alexei Marqueen, 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 received a report that an airplane powered by GE Model CF34-3B engines experienced an uncommanded simultaneous dual engine in-flight shutdown. The engine manufacturer investigation revealed evidence of corrosion in the HPC module. Further analysis indicated corrosion in the HPC case vane boreholes traditionally associated with hardware that has been exposed to a saline environment, and pitting along the HPC case, with the worst corrosion in later stages from additional oxidation due to higher operating temperatures. While the investigation has yet to identify a definitive root cause, GE considers corrosion to be a contributing factor. Corrosion in the HPC case ( printed page 23378) variable vane spindle bores can result in restricted range of motion of the VG system, which can lead to compressor instability at or below idle speeds and potential loss of engine thrust control. As a result, GE published service material with inspection instructions to determine if the VG actuating system is obstructed by corrosion that can reduce its range of motion. This condition, if not addressed, could result in loss of engine thrust control and reduced control of the airplane.

The affected population of engines includes the entire GE Model CF34-3 fleet. GE Model CF34-1A engines have all been converted to CF34-3A or they are no longer in production or service, but they are included in the applicability of this proposed AD in case there are any remaining GE Model CF34-1A engines that are unaccounted for.

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 GE CF34BJ Service Bulletin 72-0347, Revision 02, dated October 30, 2025. This material specifies procedures for performing repetitive engine heat soak restart tests for a hung start and, depending on the results of the tests, engine troubleshooting and corrective actions. This material also specifies procedures for performing a borescope inspection (BSI) of the HPC case for corrosion and, depending on the results of the BSI, a VG system functional check for pressure evaluation. This material also specifies procedures for performing a force gage test on the feedback cable for tightness and a visual inspection of the VG system for obstruction.

The FAA also reviewed MM 05-21-00, ENGINE MAINTENANCE PROGRAM from GE CF34-3 Maintenance Manual SEI-580, Rev. 49, dated August 1, 2024 (GE Model CF34-1A, CF34-3A, and CF34-3A2 engines); SM 05-21-00, MAINTENANCE PROGRAMS from GE CF34-3 Service Manual SEI-780, Rev. 65, dated February 1, 2025 (GE Model CF34-3A1 and CF34-3B engines); and EM 05-21-00 ENGINE—MAINTENANCE PROGRAM from GE CF34RJ Engine Manual SEI-756, Rev. 69, dated February 1, 2025 (GE Model CF34-3A1 and CF34-3B1 engines). This material specifies procedures for performing VG system inspections on certain GE Model engines, as applicable.

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 performing repetitive engine heat soak restart tests for a hung start and, depending on the results of the tests, engine troubleshooting and corrective actions. This proposed AD would also require performing a borescope inspection (BSI) of the HPC case for corrosion and, depending on the results of the BSI, a VG system functional check for pressure evaluation. This proposed AD would also require, depending on inspection results, performing a force gage test on the feedback cable for tightness and a visual inspection of the VG system for obstruction and, if necessary, removal of the engine from service. This proposed AD would also require revising the ALS of the existing engine maintenance manual to incorporate the VG system functional check.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would affect 1,152 engines installed on airplanes of U.S. registry.

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

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

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 ( printed page 23379) 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.

The Proposed Amendment

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

1. The authority citation for part 39 continues to read as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701.

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

General Electric Company: Docket No. FAA-2026-3875; Project Identifier AD-2025-01365-E.

(a) Comments Due Date

The FAA must receive comments on this airworthiness directive (AD) by June 15, 2026.

(b) Affected ADs

None.

(c) Applicability

This AD applies to the following General Electric Company (GE) Model engines:

(1) CF34-1A, CF34-3A, and CF34-3A2 engines with engine serial numbers (ESN) 350103 through 350525.

(2) CF34-3A1 engines with ESN 807001 through 807661.

(3) CF34-3B engines with ESN 872001 through 873999, 950000 through 950999, and 801001 through 801714.

(d) Subject

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

(e) Unsafe Condition

This AD was prompted by a dual engine power loss event and consequent manufacturer investigation, which revealed corrosion in the high-pressure compressor (HPC) case affecting the variable geometry (VG) system. The FAA is issuing this AD to detect corrosion in the HPC case that can restrict VG system movement, which can lead to compressor instability at or below idle speeds. The unsafe condition, if not addressed, could result in loss of engine thrust control and reduced control of the airplane.

(f) Compliance

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

(g) Definitions

For the purpose of this AD:

(1) Group 1 engines are engines with 12 months rolling average utilization of less than 250 hours per year.

(2) Group 2 engines are engines with 12 months rolling average utilization of more than 250 hours per year.

(3) Group 3 engines are spare engines or engines that are switched between two different aircraft tail numbers.

(h) Required Actions

(1) Within 3 months after the effective date of this AD and every 3 months thereafter, perform an engine heat soak restart test on each engine in accordance with the Accomplishment Instructions, paragraph 3.B.(1), of GE Service Bulletin (SB) CF34-BJ 72-0347 Revision 02, dated October 30, 2025 (GE SB CF34-BJ 72-0347 R02). If a hung start is experienced, before further flight, troubleshoot the engine in accordance with the Accomplishment Instructions, paragraph 3.B.(2), of GE SB CF34-BJ 72-0347 R02.

(2) Within the applicable time specified in paragraphs (h)(2)(i) through (iii) of this AD, perform a borescope inspection (BSI) of the high-pressure compressor (HPC) case in accordance with the Accomplishment Instructions, paragraph 3.C, of GE SB CF34-BJ 72-0347 R02. If the applicable engine group cannot be determined due to lack of available data, use Group 1 engines as the applicable condition for the engine.

(i) For Group 1 engines, within 12 months after the effective date of this AD.

(ii) For Group 2 engines, within 24 months after the effective date of this AD.

(iii) For Group 3 engines, before further flight after the effective date of this AD.

(3) If, during the heat soak restart test or the engine troubleshooting required by paragraph (h)(1) of this AD, or during the BSI required by paragraph (h)(2) of this AD, corrosion is found, before further flight, perform a variable geometry (VG) system functional check in accordance with the Accomplishment Instructions, paragraph 3.D, of GE SB CF34-BJ 72-0347 R02.

(4) If, during the VG system functional check required by paragraph (h)(3) of this AD, the pressure necessary to fully extend or fully retract the actuator is more than 65 psi (448 kPa), before further flight, perform a force gage test on the feedback cable and a visual inspection of the VG system in accordance with the Accomplishment Instructions, paragraph 3.E.(1)(a) and 3.E.(1)(a)(1), of GE SB CF34-BJ 72-0347 R02. If a tight feedback cable or an obstruction in the VG system is found, before further flight, repair the part in accordance with the Accomplishment Instructions, paragraph 3.E.(1)(a)(1), of GE SB CF34-BJ 72-0347 R02.

(5) If, after performing the actions required by paragraph (h)(4) of this AD, the pressure necessary to fully extend or fully retract the actuator is more than 65 psi (448 kPa), remove the engine from service.

(6) Within 12 months after the effective date of this AD, revise the Airworthiness Limitations Section (ALS) of the existing CF34-3 Business Jet Engine Manual and the operator's existing approved maintenance program or inspection program, as applicable, by incorporating the information specified in Section 9. of MM 05-21-00, ENGINE MAINTENANCE PROGRAM from GE CF34-3 Maintenance Manual SEI-580, Rev. 49, dated August 1, 2024, and Section 8. of SM 05-21-00, MAINTENANCE PROGRAMS from GE CF34-3 Service Manual SEI-780, Rev. 65, dated February 1, 2025.

(7) Within 12 months after the effective date of this AD, revise the ALS of the existing CF34-3 Regional Jet (RJ) EM and the operator's existing approved maintenance program or inspection program, as applicable, by incorporating the information specified in Section 11. of EM 05-21-00 ENGINE—MAINTENANCE PROGRAM from GE CF34RJ Engine Manual SEI-756, Rev. 69, dated February 1, 2025.

(i) Terminating Action

Performing a BSI of the HPC case in accordance with paragraph (h)(2) of this AD constitutes terminating action for the repetitive heat soak test restart required by paragraph (h)(1) of this AD for Group 1 or Group 2 engines, as applicable. Group 3 engines are not subject to repetitive heat soak restart tests.

(j) Credit for Previous Actions

You may take credit for the actions required by paragraphs (h)(1) through (5) of this AD if you removed and repaired the following part numbers (P/N) within 48 months prior to the effective date of this AD using GE SEI-582, 72-31-00, REPAIR, dated September 15, 2001; or GE SEI-782, HMM 72-32-16, REPAIR 07, Rev 65, dated February 1, 2025; or GE SEI-782, HMM 72-32-17, REPAIR 07, Rev 65, dated February 1, 2025, at an approved Maintenance Repair and Overhaul (MRO) shop: ( printed page 23380)

(1) HPC lower case P/N 6040T84P01 and 6052T48P01.

(2) HPC upper case P/N 6040T84P02 and 6052T48P02.

(3) Compressor case assemblies P/N 4922T71G01, 5088T55G01, 5088T55G02, 5088T55G03, 6078T70G01, 6078T70G02, and 6078T70G03.

(k) 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 (l)(2) 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.

(l) Additional Information

(1) For more information about this AD, Alexei Marqueen, Aviation Safety Engineer, FAA, 2200 South 216th Street, Des Moines, WA 98198; phone: (781) 238-7178; email: alexei.t.marqueen@faa.gov.

(2) Material identified in this AD that is not incorporated by reference is available at the address specified in paragraph (m)(3) of this AD.

(m) 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) GE CF34-BJ Service Bulletin 72-0347, Revision 02, dated October 30, 2025.

(ii) MM 05-21-00, ENGINE MAINTENANCE PROGRAM from GE CF34-3 Maintenance Manual SEI-580, Rev. 49, dated August 1, 2024.

(iii) SM 05-21-00, MAINTENANCE PROGRAMS from GE CF34-3 Service Manual SEI-780, Rev. 65, dated February 1, 2025.

(iv) EM 05-21-00 ENGINE—MAINTENANCE PROGRAM from GE CF34RJ Engine Manual SEI-756, Rev. 69, dated February 1, 2025.

(3) For GE material identified in this AD, contact General Electric Company, 1 Neumann Way, Cincinnati, OH 45215; phone: (513) 552-3272; email: aviation.fleetsupport@ge.com; website: ge.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.

91 FR 23377