COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES McDonnell Douglas (Hughes) and Kawasaki 369 Series Helicopters AD/HU 369/78 Four Bladed Tail Rotor Hubs 11/89 DM Applicability: All MDHC 369D and 369E series helicopters fitted with four-bladed tail rotor hub P/N 369D21700-3 unless the currently fitted hub has been previously inspected in accordance with the Requirement Document. Requirement: Inspect the tail rotor hub in accordance with MDHC S.I.N. DN-160 or EN-50 as applicable. Note: Maintenance organisations will note MDHCs offer to replace unserviceable items free of charge and are urged to inspect their spares inventory forthwith. Compliance: 1. Helicopters with hub serial numbers 196 through 251 - before the accumulation of 10 hours component time in service after 11 September 1989. 2. All other affected helicopters - before the accumulation of 100 hours component time in service after 11 September 1989. Background: One hub has been returned from service with fatigue cracks. MDHC has determined that the cracks are a result of electrical arcing caused by poor anode contact during the Tiodize coating process during manufacture.