COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES DHC-6 (Twin Otter) Series Aeroplanes AD/DHC-6/7 Amdt 1 Elevator Rear Spar - Inspection and Modification 1/68 Applicability: All Models With S/Nos. 1 To 105. Document: De Havilland Of Canada Mod. Bulletins 6/1134 And 6/1135. Compliance: Inspect In Accordance With Mod. Bulletin 6/1134 At Intervals Not Exceeding 50 Hours Time In Service Until Modified To Bulletin 6/1134 Or 6/1135. Modify In Accordance With Mod. Bulletin 6/1135 Before 1 April 1968.