AD Proposed for Hiller UH-12E Main Rotor Driveshaft

The FAA has proposed adopting a new Airworthiness Directive (AD) for Hiller Model UH-12E and UH-12E-L helicopters. 

The FAA received a report of two cracks in a main rotor (M/R) drive shaft that were found during an inspection involving a Siam Hiller Model UH-12E helicopter. These cracks resulted from hydrogen embrittlement, possibly due to improper baking after the electroplating process, and certain paint strippers exploiting galvanic potential between the steel and cadmium. Since the affected part may also be installed on Model UH-12E-L helicopters, this model helicopter is also affected by this unsafe condition. 

This proposed AD would require, with the M/R drive shaft removed, removing the coatings from all surfaces of the M/R drive shaft by using certain paint strippers, hydrogen embrittlement relief baking the M/R drive shaft, and performing a magnetic particle inspection of the M/R drive shaft for a crack. Depending on the results of the magnetic particle inspection, this proposed AD would require removing the M/R drive shaft from service and installing an airworthy part. This proposed AD would also prohibit installing an affected M/R drive shaft on any helicopter unless the actions required by this proposed AD have been accomplished and prohibit using certain paint removers on the M/R drive shaft. 

Comments are due February 28, 2025. You can find the proposed AD here.