COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Cessna 185 Series Aeroplanes AD/CESSNA 185/35 Vertical Fin Rear Spar 12/80 Applicability: Model 185 with S/Nos. 18502311 to 18504070. Requirement: Action in accordance with Cessna SIL No. SE80-85. Compliance: Within 100 hours time in service after 31 December 1980. Background: Overseas, cracks have been found in the flanges and web of the spar below the lower rudder hinge.