Airworthiness directives › 2025-15-02
AD 2025-15-02 Airworthiness Directives; Siam Hiller Holdings, Inc.
Applicability*9
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.
Compliance
Comply with this AD within the compliance times specified, unless already done.
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.
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.
Affected ADs
None.
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