The FAA proposes to adopt a new airworthiness directive (AD) for certain CFM International, S.A. (CFM) Model CFM56-5B, CFM56-5C, and CFM56-7B engines with a certain high-pressur...
The FAA proposes to adopt a new airworthiness directive (AD) for certain CFM International, S.A. (CFM) Model CFM56-5B, CFM56-5C, and CFM56-7B engines with a certain high-pressure turbine (HPT) inner stationary seal installed. This proposed AD was prompted by multiple reports of honeycomb separation from the surface of HPT inner stationary seals. This proposed AD would require initial and repetitive borescope inspections (BSIs) of the rotating air HPT front seal for cracks and, depending on the results, replacement with a part eligible for installation. This proposed AD would also require removal and replacement of the affected HPT inner stationary seal. This proposed AD would also require inspection of the affected HPT inner stationary seal for honeycomb separation and, depending on the results of the inspection, removal and replacement of the rotating air HPT front seal, HPT rotor blades, and No. 3 ball bearing. 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 October 29, 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-2026-8803; 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:
For CFM service material identified in this proposed AD, contact CFM GE Aviation Fleet Support, 1 Neumann Way, M/D Room 285, Cincinnati, OH 45125; phone: (877) 432-3272; email:aviation.fleetsupport@ge.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:
Alexei Marqueen, Aviation Safety Engineer, FAA, 2200 South 216th Street, Des Moines, WA 98198; phone: (781) 238-7178; email:
alexei.t.marqueen@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-2026-8803; Project Identifier AD-2026-00385-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
( printed page 58043)
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 was notified by the manufacturer of multiple reports of honeycomb separation from the surface of HPT inner stationary seals. A manufacturer investigation revealed that the affected HPT inner stationary seal may not have gone through the correct braze repair process, which could lead to a localized separation of the replaced honeycomb. This separation could affect the life of the HPT forward outer seal because missing honeycomb can induce a vibratory response in the HPT forward outer seal resulting in crack initiation in the seal teeth that propagate radially. This condition, if not addressed, could result in uncontained part 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 the following service material:
CFM Service Bulletin (SB) SB CFM56-7B S/B 72-1096, Revision 01, dated January 21, 2026.
This service material, differentiated by engine model, specifies procedures for performing a BSI of the rotating air HPT front seal for cracks and other damage.
The FAA also reviewed the following service material:
This service material, differentiated by engine model, specifies procedures for inspecting the HPT inner stationary seal for honeycomb separation.
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 initial and repetitive BSIs of the rotating air HPT front seal for cracks and other damage and, depending on the results, replacement with a part eligible for installation. This proposed AD would also require removal and replacement of the affected HPT inner stationary seal. This proposed AD would also require inspection of the affected HPT inner stationary seal for honeycomb separation and, depending on the results of the inspection, removal and replacement of the rotating air HPT front seal, HPT rotor blades, and No. 3 ball bearing.
Costs of Compliance
The FAA estimates that this AD, if adopted as proposed, would affect 39 engines installed on airplanes of U.S. registry.
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
BSI of rotating air HPT front seal
8 work-hours × $85 per hour = $680
$0
$680
$26,520
Replacement of HPT inner stationary seal
8 work-hours × $85 per hour = $680
173,700
174,380
6,800,820
Inspection of HPT inner stationary seal
8 work-hours × $85 per hour = $680
0
680
26,520
The FAA estimates the following costs to do any necessary replacements that would be required based on the results of the proposed inspections. The agency has no way of determining the number of engines that might need these replacements:
On-Condition Costs
Action
Labor cost
Parts cost
Cost per
product
Replacement of rotating air HPT front seal
8 work-hours × $85 per hour = $680
$601,400
$602,080
Replacement of HPT rotor blades (set)
8 work-hours × $85 per hour = $680
2,019,320
2,020,000
Replacement of No. 3 ball bearing
8 work-hours × $85 per hour = $680
70,460
71,140
( printed page 58044)
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:
(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 FAA must receive comments on this airworthiness directive (AD) by October 29, 2026.
(b) Affected ADs
None.
(c) Applicability
This AD applies to CFM International, S.A. (CFM) Model engines identified in table 1 to paragraph (c) of this AD with an installed high-pressure turbine (HPT) inner stationary seal, part number (P/N) 1808M56G01, with a serial number (S/N) listed in Paragraph 4., APPENDIX—A, Table 3, of CFM Service Bulletin (SB) CFM56-5B S/B 72-1125, Revision 02, dated January 19, 2026 (CFM56-5B S/B 72-1125 R02); Paragraph 4., APPENDIX—A, Table 3, of CFM SB CFM56-5C S/B 72-0811, Revision 02, dated January 19, 2026 (CFM56-5C S/B 72-0811 R02); or Paragraph 4., APPENDIX—A, Table 3, of CFM SB CFM56-7B S/B 72-1093, Revision 02, dated January 19, 2026 (CFM56-7B S/B 72-1093 R02).
This AD was prompted by multiple reports of honeycomb separation from the surface of HPT inner stationary seals. The FAA is issuing this AD to prevent failure of the HPT inner stationary seal and the rotating air HPT front seal. The unsafe condition, if not addressed, could result in uncontained part 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) Definitions
For the purpose of this AD:
(1) Group 1 engines are CFM Model CFM56-5B engines with a rotating air HPT front seal (HPT front seal) installed having P/N 1795M36P01 or P/N 1795M36P02, and an HPT inner stationary seal installed having P/N 1808M56G01, with an S/N listed in Paragraph 4., APPENDIX—A, Table 1, of CFM56-5B S/B 72-1129, Revision 01, dated January 21, 2026 (CFM56-5B S/B 72-1129, Revision 01).
(2) Group 2 engines are CFM Model CFM56-5B engines with an HPT front seal installed having P/N 1795M36P01 or P/N 1795M36P02, and an HPT inner stationary seal installed having P/N 1808M56G01, with an S/N listed in Paragraph 4., APPENDIX—A, Table 2, of CFM56-5B S/B 72-1129, Revision 01.
( printed page 58045)
(3) Group 3 engines are CFM Model CFM56-5C engines with an installed HPT inner stationary seal, P/N 1808M56G01, with an S/N listed in Paragraph 4., APPENDIX—A, Table 1, of CFM56-5C S/B 72-0813, Revision 01, dated June 9, 2026 (CFM56-5C S/B 72-0813, Revision 01).
(4) Group 4 engines are CFM Model CFM56-7B engines with an HPT front seal installed having P/N 1795M36P02, and an HPT inner stationary seal installed having P/N 1808M56G01, with an S/N listed in Paragraph 4., APPENDIX—A, Table 1, of CFM56-7B S/B 72-1096 Revision 01, dated January 21, 2026 (CFM56-7B S/B 72-1096, Revision 01).
(5) Group 5 engines are CFM Model CFM56-7B engines with an HPT front seal installed having P/N 1795M36P02 and an HPT inner stationary seal installed having P/N 1808M56G01, with an S/N listed in Paragraph 4., APPENDIX—A, Table 2, of CFM56-7B S/B 72-1096 Revision 01.
(6) An “engine shop visit” is the induction of an engine into the shop for maintenance involving the separation of pairs of major mating engine case flanges, except for the following situations, which do not constitute an engine shop visit:
(i) Separation of engine flanges solely for the purpose of transportation of the engine without subsequent maintenance.
(ii) Separation of engine flanges solely for the purpose of replacing the fan or propulsor without subsequent maintenance.
(7) An “HPT inner stationary seal that is eligible for installation” is an HPT inner stationary seal:
(i) That is not listed in Table 3 of CFM56-5B S/B 72-1125 R02; Table 3 of CFM56-5C S/B 72-0811 R02; or Table 3 CFM56-7B S/B 72-1093 R02; or
(ii) With P/N 1808M56G01 and an S/N listed in Table 3 of CFM56-5B S/B 72-1125 R02; Table 3 of CFM56-5C S/B 72-0811 R02; or Table 3 CFM56-7B S/B 72-1093 R02, that has been repaired as specified in CFM56—5B Engine Shop Manual (ESM), 72—41—03, REPAIR 003; CFM56—5C ESM, 72—41—03, REPAIR 003; or CFM56—7B ESM, 72—41—03, REPAIR 003, after the repair date listed in Paragraph 4., APPENDIX—A, Table 3 of CFM56-5B S/B 72-1125 R02, CFM56-5C S/B 72-0811 R02, or CFM56-7B S/B 72-1093 R02, as applicable by engine model.
(8) A “rotating air HPT front seal that is eligible for installation” is any rotating air HPT front seal that was not removed from service as a result of paragraph (h)(2) of this AD or as a result of paragraph (h)(5)(i) of this AD.
(9) “HPT rotor blades eligible for installation” are new HPT rotor blades with zero flight hours since new or HPT rotor blades that have been inspected and returned to a serviceable condition using FAA-approved maintenance procedures.
(10) A “No. 3 ball bearing eligible for installation” is any No. 3 ball bearing that was not removed from service as a result of paragraph (h)(5)(iii) of this AD.
(h) Required Actions
(1) Within the applicable time specified in paragraphs (h)(1)(i) through (v) of this AD, perform repetitive borescope inspections (BSI) of the HPT front seal in accordance with the Accomplishment Instructions, paragraph 3.B of CFM56-5B S/B 72-1129, Revision 01; CFM56-5C S/B 72-0813, Revision 01; or CFM56-7B S/B 72-1096, Revision 01, as applicable by engine model.
(i) For Group 1 engines, within 400 flight cycles (FCs) after the effective date of this AD and thereafter at intervals not to exceed 800 FCs.
(ii) For Group 2 engines, within 300 FCs after the effective date of this AD and thereafter at intervals not to exceed 800 FCs.
(iii) For Group 3 engines, within 125 FCs after the effective date of this AD and thereafter at intervals not to exceed 250 FCs.
(iv) For Group 4 engines, within 400 FCs after the effective date of this AD and thereafter at intervals not to exceed 800 FCs.
(v) For Group 5 engines, within 300 FCs after the effective date of this AD and thereafter at intervals not to exceed 800 FCs.
(2) If during any BSI required by paragraph (h)(1) of this AD any crack is detected, before further flight, remove the rotating air HPT front seal from service and replace with a rotating air HPT front seal that is eligible for installation.
(3) At the next engine shop visit after the effective date of this AD, remove the affected HPT inner stationary seal and replace it with an HPT inner stationary seal that is eligible for installation.
(4) After removing the affected HPT inner stationary seal required by paragraph (h)(3) of this AD, inspect the removed HPT inner stationary seal for honeycomb separation in accordance with the Accomplishment Instructions, paragraph 3.C.(1), of CFM56-5B S/B 72-1125 R02; CFM56-5C S/B 72-0811 R02; or CFM56-7B S/B 72-1093 R02, as applicable by engine model.
(5) If honeycomb separation is found during the inspection required by paragraph (h)(4) of this AD, before further flight:
(i) Remove the rotating air HPT front seal from service and replace with a rotating air HPT front seal that is eligible for installation.
(ii) Remove the HPT rotor blades and replace them with HPT rotor blades eligible for installation.
(iii) Remove the No. 3 ball bearing from service and replace with a No. 3 ball bearing eligible for installation.
(i) Terminating Action
Accomplishing the actions in paragraphs (h)(3) through (5) of this AD constitutes terminating action for the repetitive BSIs of the HPT front seal required by paragraph (h)(1) of this AD.
(j) Installation Prohibition
(1) After the effective date of this AD, do not reinstall any rotating air HPT front seal that was removed as a result of paragraphs (h)(2) or (h)(5)(i) of this AD on any engine.
(2) After the effective date of this AD, do not reinstall any No. 3 ball bearing that was removed as a result of paragraph (h)(5)(iii) of this AD on any engine.
(k) No Reporting Requirement
Although the service material specifies to submit certain information to the manufacturer, this AD does not require that action.
(l) Credit for Previous Actions
You may take credit for the initial BSI specified in paragraph (h)(1) of this AD if you performed that BSI before the effective date of this AD using CFM SB CFM56-5C S/B 72-0813, Revision 00, dated July 15, 2025, CFM56-5B S/B 72-1129 Revision 00, dated July 10, 2025, or CFM56-7B S/B 72-1096 Revision 00, dated July 10, 2025.
You may take credit for the actions specified in paragraphs (h)(3) through (5) of this AD if you performed those actions before the effective date of this AD using CFM56-5B S/B 72-1125 Revision 00, dated January 28, 2025; CFM56-5B S/B 72-1125 Revision 01, dated July 10, 2025; CFM56-5C S/B 72-0811 Revision 00, dated January 28, 2025; CFM56-5C S/B 72-0811 Revision 01, dated July 10, 2025; CFM56-7B S/B 72-1093 Revision 00, dated January 28, 2025; or CFM56-7B S/B 72-1093 Revision 01, dated July 10, 2025.
(m) 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 (n)(1) 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.
(n) Additional Information
(1) For more information about this AD, contact 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) For material identified in this AD that is not incorporated by reference, contact CFM GE Aviation Fleet Support, 1 Neumann Way, M/D Room 285, Cincinnati, OH 45125; phone: (877) 432-3272; email:
aviation.fleetsupport@ge.com.
(o) 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) CFM Service Bulletin (SB) CFM56-5B S/B 72-1125, Revision 02, dated January 19, 2026.
(ii) CFM SB CFM56-5B S/B 72-1129, Revision 01, dated January 21, 2026.
(3) For CFM material identified in this AD, contact CFM GE Aviation Fleet Support, 1 Neumann Way, M/D Room 285, Cincinnati, OH 45125; phone: (877) 432-3272; email:
aviation.fleetsupport@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.
14 CFR 11.43
5 U.S.C. 552
www.archives.gov/federal-register/cfr/ibr-locations