2026-13781: Airworthiness Directives; Restricted Category Model CH-47D Helicopters

Federal Register, Volume 91 Issue 129 (Wednesday, July 8, 2026) [Federal Register Volume 91, Number 129 (Wednesday, July 8, 2026)] [Proposed Rules] [Pages 42144-42149] From the Federal Register Online via the Government Publishing Office [www.gpo.gov] [FR Doc No: 2026-13781] ======================================================================= ----------------------------------------------------------------------- DEPARTMENT OF TRANSPORTATION Federal Aviation Administration 14 CFR Part 39 [Docket No. FAA-2025-5394; Project Identifier AD-2025-01194-R] RIN 2120-AA64 Airworthiness Directives; Restricted Category Model CH-47D Helicopters

Agency

Federal Aviation Administration (FAA), DOT.

Action

Supplemental notice of proposed rulemaking (SNPRM). -----------------------------------------------------------------------

Summary

The FAA is revising a notice of proposed rulemaking (NPRM) that would have applied to all restricted category Model CH-47D helicopters. This proposed action would revise the NPRM by expanding the required actions paragraph applicable to all right-hand (RH) forward transmission support beam fittings with any part number, narrowing the area of inspection, and increasing the reporting requirement compliance times. The FAA is proposing this airworthiness directive (AD) to address the unsafe condition on these products. Since these actions would impose an additional burden over those in the NPRM and to address some commenters' concerns, the agency is requesting comments on this SNPRM.

Dates

The FAA must receive comments on this SNPRM by August 24, 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-2025-5394; 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 SNPRM, any comments received, and other information. The street address for Docket Operations is listed above.

For Further Information Contact

Taffy Shenoy, Aviation Safety Engineer, FAA, 3960 Paramount Boulevard, Lakewood, CA 90712; phone: (206) 231-3559; email: [email protected].

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 ADDRESSES. Include ``Docket No. FAA-2025-5394; Project Identifier AD-2025-01194-R'' 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 again revise the 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 [[Page 42145]] will also post a report summarizing each substantive verbal contact received about this SNPRM. 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 SNPRM 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 SNPRM, 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 SNPRM. Submissions containing CBI should be sent to Taffy Shenoy, Aviation Safety Engineer, FAA, 3960 Paramount Boulevard, Lakewood, CA 90712. 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 issued an NPRM to amend 14 CFR part 39 by adding an AD that would have applied to all restricted category Model CH-47D helicopters. The NPRM was published in the Federal Register on December 22, 2025 (90 FR 59764). The NPRM was prompted by reports of fatigue cracking of the RH forward transmission support beam fitting having part number 145S1838-1. In the NPRM, the FAA proposed to require repetitively inspecting the RH forward transmission support beam fitting for cracking, and depending on the results, repairing any crack(s) or replacing parts. In the NPRM, the FAA also proposed to require submitting data on any previous repairs and replaced fittings. Actions Since the NPRM Was Issued Since the FAA issued the NPRM, several comments have been received, and the FAA has determined to revise the NPRM by making the actions in paragraph (g) of this proposed AD applicable to all RH forward transmission support beam fittings with any part number, narrowing the area of inspection by defining the station range and butt-line location, and increasing the reporting requirement compliance time. Additionally, new information received during the comment period from a type certificate holder identified crack findings in fittings with part number 145S1838-6, further supporting the expansion of applicability to all part numbers. The comment disposition below explains and addresses these comments. Due to these comments and the FAA's response to the comments, the FAA determined some of the requests expanded the scope of the proposed AD. The FAA is proposing this AD to detect and address fatigue cracking of the RH forward transmission support beam fittings. The unsafe condition, if not addressed, could result in crack propagation and lead to failure of the RH forward transmission support beam fitting, excessive vibration, and loss of control of the helicopter. Comments The FAA received comments from seven commenters. The commenters were an anonymous individual; Billings Flying Service; Coulson Aviation; Design Analysis Certification Aerospace (DACA); PJ Helicopters, Inc.; Tandem Rotor, LLC; and Vertical Aviation International. The following discussion presents the comments received on the NPRM and the FAA's response to these comments. DACA also submitted additional comments that are not related to this proposed AD and did not suggest any changes. Vertical Aviation International supported the NPRM without change. Requests To Withdraw the NPRM An anonymous individual requested the FAA withdraw the NPRM because the aged airframe no longer requires further restrictions. Billings Flying Service requested the FAA withdraw the NPRM because the existing maintenance program and repair infrastructure for these restricted category aircraft have been shown to find and address the cracks. Billings Flying Service and Tandem Rotor, LLC requested the FAA withdraw the NPRM due to the lack of relevant technical data and that no data has been shown detailing this is a frequently occurring unsafe condition rather than limited infrequent repairs, nor is data present confirming the contributing factors. DACA requested the FAA withdraw the NPRM and not issue an AD until ``certification bodies'' accept a long overdue aircraft level master data list (MDL) and its supporting analysis dataset into the restricted category type certificate (RCTC) qualifying program through a memorandum of understanding (MOU) with each of the RCTC holders. DACA stated that operators and RCTC holders should voluntarily shorten their inspection intervals through service material. DACA also requested the FAA delay final rulemaking to allow RCTC holders to further investigate the potential root cause for the cracking of the RH forward transmission support beam fitting. The FAA disagrees with the requests to withdraw the NPRM. The FAA has received data supporting its determination that an unsafe condition exists with the specified parts. Additionally, the FAA cannot rely on owners or operators voluntarily adopting certain manuals or shortening their inspection intervals. Although existing maintenance programs can possibly address cracks, the FAA finds that sufficient data exists to support the requirements of this proposed AD. This proposed AD has not been changed regarding these requests. Requests for Documentation To Be Posted in the Docket Billings Flying Service and Tandem Rotor, LLC requested the FAA provide all relevant technical data, reports of fatigue cracking, records of ex-parte contacts, decisions or reports that led to the need for this rulemaking, the substantiation of the required 100-hour inspection interval time, and corrective action determinations, to be posted in the AD docket. Billings Flying Service stated there is no evidence of the agency's analysis to determine whether the condition was caused by design miscalculations, manufacturing anomalies, the operational environment, maintenance findings, or maintenance activities. Additionally, Billings Flying Service and Tandem Rotor, LLC stated that without basic safety data uploaded in the AD docket, the NPRM lacks a record of the facts supporting its conclusion and thus fails to provide a reasonable basis for the proposed rule. Billings Flying Service requested the Corrective Action Review Board (CARB) report that supported the 100-hour time-in-service (TIS) repetitive inspection requirement be posted in the docket as evidence of the need for rulemaking. The FAA disagrees with posting decision-making documents in the AD docket. The FAA has obtained operator information indicating that mandatory action is necessary to maintain the continued operational safety of all helicopters of this type design. Furthermore, the FAA does not post pre-decisional documents in the AD docket for public view. Under the provisions of the Freedom of Information Act, 5 U.S.C. 552, these materials are not releasable because they are pre-decisional and often contain information that is proprietary to the design approval holder. Additionally, [[Page 42146]] no ex-parte records exist for this proposed AD at the time of publication of this SNPRM. This proposed AD has not been changed regarding these requests. Requests To Remove or Revise the Reporting Requirements Billings Flying Service, Tandem Rotor, LLC, and PJ Helicopters, Inc. requested the FAA remove or revise the reporting requirement as it will place an undue burden on operators. Billings Flying Service, Tandem Rotor, LLC, and PJ Helicopters, Inc., all stated that data related to previous repairs and replacement fittings are mixed between civilian and military environments and have different reporting requirements, and the TIS of these used parts have no requirement to be time-tracked per military manuals or FAA approved type certificate (TC) instructions for continued airworthiness (ICAs). Billings Flying Service and Tandem Rotor, LLC requested the FAA revise and condense paragraphs (g)(3)(i) and (ii) of the proposed AD to remove the 30-day requirement and add ``If a fitting was replaced, submit information regarding its sourcing (if available) to include but not limited to: Seller, Production Date, Producer and/or manufacturer.'' They further stated that the applicable part is not life-limited, and the serial number (if the part has one) and life status were not required to be recorded, therefore the TIS will not be readily available. Billings Flying Service and Tandem Rotor, LLC also stated that requiring operators to submit this sourcing information would be outside the regulations of 14 CFR. Additionally, Billings Flying Service and Tandem Rotor, LLC requested the FAA remove paragraph (g)(2) of the proposed AD, because for repairs that were accomplished prior to civilian certification, obtaining the data requested from the appropriate military branch within the stated timeline is likely to put the operator at an unnecessary compliance risk. Additionally, they stated that militaries have no requirement on response times, or requirement to respond at all to civilian operators, and this requirement could cause grounding aircraft in order to comply with this research request. The commenters also stated that the part is not life-limited, the serial number (if the part has one) and life status were not required to be recorded, therefore the TIS will not be readily available. Research to obtain the information would take hours and more than likely be unsuccessful in fulfilling the requirements of the proposed rule. The FAA disagrees with removing the reporting requirements in paragraphs (g)(2) or (3) of the proposed AD. The FAA also disagrees with condensing paragraphs (g)(3)(i) and (ii) of the proposed AD into one paragraph. The purpose of the reporting requirement is for the FAA to recognize if any repairs have failed and if the existing repairs provide an acceptable level of safety. The affected part TIS is the same as the airframe, since the part is not rotable. The time of removal of the used part should be recorded in maintenance records. If operators have difficulty providing military Form 2408-15, then they are able to apply for an alternative method of compliance (AMOC) in accordance with the provisions provided in paragraph (i) of the proposed AD. The FAA agrees with revising paragraph (g)(3)(ii) of this proposed AD by modifying the requirement to say ``Donor Part Seller, Donor Part Production Date, Donor Part Producer and/or Donor Part Manufacturer,'' in order to be more specific about the source. Even though the FAA disagrees with removing or combining the reporting paragraphs, the FAA has determined that an additional 30 days to report allows applicants, operators, and TC holders additional time to gather the required information. The required actions section of this proposed AD has been revised accordingly to allow 60 days for reporting. Request To Revise the Applicability Paragraph Billings Flying Service requested the FAA revise the Applicability paragraph of the NPRM, stating that the effectivity should be based on the known configuration that is proposed to be affected, specifically to part number 145S1838-1. The FAA disagrees with adding the part number to the applicability section because the part number for the installed fitting may vary by the dash number and some parts may not be labeled with the part number. Furthermore, the FAA does not know of any specific part number that is not susceptible to the subject cracking. This proposed AD has not been changed regarding this request. Request To Revise or Remove the Inspection Interval Billings Flying Service and Tandem Rotor, LLC requested the FAA revise the 100-hour TIS repetitive inspection interval because the FAA has not provided data or a summary of why the repetitive inspection interval of 100 hours is appropriate. Billings Flying Service stated an arbitrary 100-hour TIS repetitive inspection requirement burdens operators and requested further information on why the inspection interval could not be substantiated at 400 hours TIS or 800 hours TIS. Additionally, Billings Flying Service stated that if the FAA has substantiating data that there is fatigue cracking, the initial 30-hour TIS inspection is likely appropriate based upon that data. The FAA disagrees with the request to revise or remove the inspection interval. The FAA determined that the repetitive 100-hour TIS interval is necessary to allow for sufficient opportunity to detect a crack prior to failure without requiring specialized equipment and technicians while aligning with already prescribed maintenance tasks. This proposed AD has not been changed regarding this request. Request To Revise the Initial Inspection Compliance Time Coulson Aviation requested the FAA revise the compliance time for the initial inspection from 30 hours TIS to 100 hours TIS after the effective date of the proposed AD. The commenter stated an initial 30- hour TIS inspection may be unnecessarily restrictive and may not provide a safety benefit when combined with the repetitive 100-hour TIS inspection requirement. The FAA disagrees with the request. In developing an appropriate compliance time, the FAA considered the safety implications, parts availability, and normal maintenance schedules for timely accomplishment of the required inspection. If additional data are presented that would justify a longer compliance time than the required 30 hours, the FAA may consider further rulemaking on this issue. The proposed AD has not been changed regarding this request. Request To Clarify the Inspection Area in the Required Actions Paragraph Billings Flying Service stated that if the reported cracks are exclusively found to be in the forward area on the inboard face of the mount (``area of interest''), then the inspection should be conducted and specified where the damage has been found. The commenter further stated requiring full open-up and complete mount inspection every 100 hours TIS would be a significant burden to the operator, and complete access to the installed part would require significant additional maintenance. The FAA acknowledges the commenter's concern and infers that the commenter is requesting that the inspection area be clarified. The FAA agrees to clarify the inspection area in [[Page 42147]] order to provide a boundary area. Paragraph (g)(1) of the Required Actions paragraph of this proposed AD has been revised by adding, ``and from the top cap to lower termination of the fitting for cracks'' when describing the area of inspection. Request To Revise the Inspection Method To Require an Eddy Current Inspection Coulson Aviation requested that the FAA revise paragraph (g)(1) of the Required Actions paragraph of the proposed AD to require an eddy current inspection in lieu of or in addition to the visual inspection. The commenter stated that they have identified four cracked transmission beams on seven airframes and only two of these cracks were visible per the visual inspection criteria noted in the proposed AD, but all four were identified clearly via eddy current inspection. The commenter also stated that relying solely on a visual inspection may not be reliable to detect subsurface or early-stage cracking within the fitting. Furthermore, the commenter stated that without a detailed inspection method such as an eddy current inspection, the safety margin of CH-47D operations is significantly degraded. The FAA acknowledges that operators can choose to use eddy current in addition to the required detailed visual inspection or request an AMOC to use eddy current inspections instead of a detailed visual inspection. The FAA disagrees with requiring an eddy current inspection in lieu of a detailed visual inspection because a detailed visual inspection at the 100-hour TIS interval allows for sufficient opportunity to detect a crack prior to failure without requiring specialized equipment and technicians while aligning with already prescribed maintenance tasks. This proposed AD has not been changed regarding this request. Request To Revise the Costs of Compliance Paragraph Billings Flying Service stated the hour estimates as stated in the proposed rule would not allow for the additional required structure to be open to allow full access. The commenter also stated that the information required for reporting on previous repairs and replaced fittings is more extensive than the time estimated in the cost of compliance. The commenter further stated that it is not realistic to assume that operators can review the entirety of an aircraft's records in an hour because this data is not easily accessible and the records will range from paper documents to modern maintenance recordkeeping systems, resulting in extensive operational and maintenance data that would need to be combed through and analyzed. The FAA agrees and has revised the cost estimate for reporting in the Costs of Compliance paragraph of this proposed AD from one hour to five hours. Request To Revise the Special Flight Permit Paragraph Coulson Aviation requested the FAA revise paragraph (h) of the proposed AD to allow special flight permits for the purpose of relocating the aircraft to a facility capable of performing the required repair. The commenter stated that if replacement of the fitting is necessary, the repair will require substantial infrastructure, tooling, and manpower that may not be available at the aircraft's current location. Additionally, the commenter stated that prohibiting ferry flights may unnecessarily ground aircraft in locations not suitable for corrective maintenance. The FAA partially agrees. The FAA disagrees with allowing special flight permits without restriction. However, the FAA agrees that special flight permits may be requested through the AMOC process. Accordingly, paragraph (h) of this proposed AD has been revised to state, ``Special flight permits, as described in 14 CFR 21.197 and 21.199, are not allowed unless approved in accordance with the procedures specified in paragraph (i)(1) of this AD.'' FAA's Determination The FAA is proposing this AD after determining the unsafe condition described previously is likely to exist or develop in other products of the same type design. Certain changes described above expand the scope of the NPRM. As a result, it is necessary to reopen the comment period to provide additional opportunity for the public to comment on this SNPRM. Proposed AD Requirements in This SNPRM This proposed AD would require repetitively inspecting the RH forward transmission support beam fitting for cracking, and depending on the results, repairing any crack(s) or replacing parts. This proposed AD would also require submitting data on any previous repairs and replaced fittings to the FAA. Costs of Compliance The FAA estimates that this AD, if adopted as proposed, would affect 42 helicopters of U.S. registry. The FAA estimates the following costs to comply with this proposed AD: Estimated Costs ---------------------------------------------------------------------------------------------------------------- Cost on U.S. Action Labor cost Parts cost Cost per product operators ---------------------------------------------------------------------------------------------------------------- Inspect RH forward transmission 2 work-hours x $85 per $0 $170 $7,140 support beam fitting. hour = $170. Report previous repairs and replaced 5 work-hours x $85 per 0 425 17,850 fittings. hour = $425. ---------------------------------------------------------------------------------------------------------------- The FAA has received no definitive data on which to base the cost estimates for the on-condition repairs specified in this proposed AD. Paperwork Reduction Act A federal agency may not conduct or sponsor, and a person is not required to respond to, nor shall a person be subject to a penalty for failure to comply with a collection of information subject to the requirements of the Paperwork Reduction Act unless that collection of information displays a currently valid OMB Control Number. The OMB Control Number for this information collection is 2120-0056. Public reporting for this collection of information is estimated to be approximately 5 hours per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. All responses to this collection of information are mandatory. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to: [[Page 42148]] Information Collection Clearance Officer, Federal Aviation Administration, 10101 Hillwood Parkway, Fort Worth, TX 76177-1524. 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 0