COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Cessna 170, 172, F172, FR172 and 175 Series Aeroplanes AD/CESSNA 170/6 Amdt 2 Undercarriage Attachment Bolts 11/71 Applicability: Model 170, 170A and 170B. Requirement: Remove the AN7-20A bolts and the nuts attaching the inboard end of the undercarriage spring legs, and replace with new AN7-20A bolts and new nuts. Compliance: At intervals not exceeding 500 hours time in service. For aircraft which have exceeded 500 hours time in service since last bolt replacement - Within 100 hours time in service after 30 November 1971 and thereafter as above.