2025-15-02: Main Rotor Mast/Swashplate

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: 2025-15-02 Siam Hillar Holdings, Inc.: Amendment 39-23089; Docket No. FAA-2024-2555; Project Identifier AD-2024-00214-R. (a) Effective Date This airworthiness directive (AD) is effective September 24, 2025. (b) Affected ADs None. (c) Applicability This AD Applies to Siam Hiller Holdings, Inc., Model UH-12E (Army OH-23G and H-23F) and UH-12E-L helicopters, certificated in any category, with a main rotor (M/R) transmission drive shaft (drive shaft) having part number (P/N) 23600 installed. Note 1 to paragraph (c): Hiller Aircraft Corporation Main Rotor Transmission Assembly Overhaul Manual, Manual 63-20, for UH-12E Series Helicopters, accepted May 6, 2015, contains additional information pertaining to inspecting the M/R drive shaft and refers to an M/R drive shaft as a transmission M/R mast and M/R drive shaft, interchangeably. (d) Subject Joint Aircraft System Component (JASC) Code 6230, Main Rotor Mast/Swashplate. (e) Unsafe Condition This AD was prompted by reports of cracks in the M/R drive shaft. The FAA is issuing this AD to address non-conforming parts and the use of improper paint stripper; and to detect cracking of the M/R drive shaft. The unsafe condition, if not addressed, could result in separation of the M/R drive shaft and M/R blades from the helicopter and consequent loss of control of the helicopter. (f) Compliance Comply with this AD within the compliance times specified, unless already done. (g) Required Actions At the next overhaul inspection of the M/R transmission assembly or within 4 years after the effective date of this AD, whichever comes first, with the M/R drive shaft removed, inspect the M/R drive shaft by accomplishing the actions required by paragraphs (g)(1) through (3) of this AD. (1) Remove all coatings from all surfaces of the M/R drive shaft by using paint stripper TT-R-248 or TT-R-2918 Type I. (2) Hydrogen embrittlement relief bake the M/R drive shaft for 24 hours minimum at 375 °F ± 25 °F. (3) Magnetic particle inspect all surfaces of the M/R drive shaft for a crack. If there is a crack, before further flight, remove the M/R drive shaft from service and install an airworthy M/R drive shaft. Note 2 to paragraph (g): Hiller Aircraft Corporation Main Rotor Transmission Assembly Overhaul Manual, Manual 63-20, for UH-12E Series Helicopters, accepted May 6, 2015, contains additional information pertaining to inspecting the M/R drive shaft, applying appropriate coatings to the M/R drive shaft, and returning the helicopter to service. (h) Parts Installation Limitations (1) As of the effective date of this AD, do not install an M/R drive shaft having P/N 23600 on any helicopter unless the actions required by paragraphs (g)(1) through (3) of this AD have been accomplished. (2) As of the effective date of this AD, do not use any paint stripper other than TT-R-248 or TT-R-2918 Type I to remove coatings from all areas of the M/R drive shaft. (i) Alternative Methods of Compliance (AMOCs) (1) The Manager, West Certification 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 West Certification Branch, send it to the attention of the person identified in paragraph (j)(1) of this AD and email to: AMOC@faa.gov. (2) 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 (1) For more information about this AD, contact Eduardo Orozco-Duran, Aviation Safety Engineer, FAA, 3960 Paramount Boulevard, Lakewood, CA 90712; phone: (562) 627-5264; email: eduardo.orozco-duran@faa.gov . (2) For Hiller Aircraft Corporation material identified in this AD that is not incorporated by reference, contact Hiller Aircraft Corporation, 925 M Street, Firebaugh, CA 93622; phone: (559) 659-5959; or website: hilleraircraftcorporation.com/. (k) Material Incorporated by Reference None. Issued on August 15, 2025. Steven W. Thompson, Acting Deputy Director, Compliance & Airworthiness Division, Aircraft Certification Service. [FR Doc. 2025-15839 Filed 8-19-25; 8:45 am]BILLING CODE 4910-13-P