COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Hiller UH-12 Series Helicopters AD/HILLER 12/36 Amdt 1 Main Drive Torsion Coupling P/N 21047-15 - Inspection of Lower Plate 10/82 Applicability: All Hiller UH-12E series, UH-12L series, OH-23G, OH-23F helicopters, fitted with a torsion coupling P/N 21047-15. Requirement: Conduct a fluorescent penetrant inspection of the lower half of the coupling, around the entire perimeter of the base where the eight cut out windows are located between the wear sleeve and the lower flange to which the rubber is bonded. FAA AD 82-16-07 refers. Compliance: Within 10 hours' time in service after 4 August 1982, and thereafter at periods not exceeding 50 hours' time in service. Background: Due to a possible manufacturing defect, all P/N 21047-15 couplings are to be inspected for cracks in the area of the lower plate windows. There have been two cracked couplings reported on local helicopters.