COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Beechcraft 77 (Skipper) Series Aeroplanes AD/BEECH 77/6 Engine Mount Assembly to Firewall Attach Bolts 12/80 Applicability: All model 77 with S/Nos. WA-1 to WA-156, WA-158 to WA-161, WA-163 to WA- 171, WA-173, WA-174, WA-177 and WA-178. Requirement: Action in accordance with Beechcraft SI No. 1153. Note: FAA AD 80-21-10 refers. Compliance: Within 25 hours' time in service after 30 October 1980. Background: The engine mount assembly attachment bolts and barrel nuts may have threads which were damaged at initial factory installations.