Helicopter Main Rotor Drive Shaft Inspection Requirements

|2025-15839|No deadline
View on Federal Register

Summary

The FAA is adopting a new airworthiness directive (AD) for certain Siam Hiller Holdings, Inc. (Siam Hiller), Model UH-12E (Army OH-23G and H-23F) and UH-12E-L helicopters. This AD was prompted by reports of cracks found in a main rotor (M/R) transmission drive shaft (drive shaft). This AD requires inspecting certain M/R drive shafts for a crack, prohibits installing certain M/R drive shafts unless the inspection is done, and prohibits using certain paint strippers. The FAA is issuing this AD to address the unsafe condition on these products.

Compliance Requirements

  1. #1

    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.; 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.; Hydrogen embrittlement relief bake the M/R drive shaft for 24 hours minimum at 375° F ± 25° F.; 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.; 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.; 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.

    Deadline: Within 4 years after effective date or next M/R transmission assembly overhaul inspection, whichever comes first

Market Impacts

  • Prohibition on installing M/R drive shafts with P/N 23600 unless specific inspection and treatment procedures are completed, restricting parts availability and installation practices; Mandatory use of specific paint strippers (TT-R-248 or TT-R-2918 Type I) for coating removal from M/R drive shafts, creating market demand for these specific products; Creatures operational barriers for helicopter operators who must comply with 4-year inspection timeline or next overhaul inspection, potentially grounding aircraft during compliance activities

Validated Company Impacts

AIRScore: 100%

AAR CORP

AAR CORP operates in the aviation aftermarket sector with significant business in parts supply and repair/engineering services, directly aligning with the AD's requirements for inspecting, maintaining, and replacing helicopter components. The company's role in distributing aircraft parts and providing maintenance services means it would be directly affected by the prohibition on installing non-compliant M/R drive shafts and the mandatory use of specific paint strippers. The rule's focus on specific helicopter maintenance procedures and paint stripper requirements has minimal alignment with the company's disclosed risk factors, which center on financial agreements, parts refurbishment dependencies, and contract compliance rather than detailed technical maintenance mandates.