COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Cessna 207 Series Aeroplanes AD/CESSNA 207/4 Exhaust Manifold Heat Exchanger 6/71 Applicability: All turbocharged models. Requirement: Action in accordance with Cessna SL No. SE71-11. Compliance: Within 50 hours time in service after 9 June 1971 and thereafter at intervals not exceeding 50 hours time in service.