COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Pilatus Porter PC-6 Series Aeroplanes AD/PC-6/43 Aileron Attachment Bracket 4/97 Applicability: Pilatus PC-6 Porter / Turbo Porter up to Serial No. 815 Requirement: Modify aileron/ flap mountings in accordance with Pilatus Service Bulletin (SB) No. 138, Rev. 2. Note: Swiss FOA AD HB 84-023 refers. Compliance: Unless already accomplished, within 100 hours time in service from 27 March 1997. This Airworthiness Directive becomes effective on 27 March 1997. Background: Cracks have been found in the angle brackets forming the attachment of the aileron flap mountings. The cracks have been attributed to fatigue caused by the aircraft being subjected to overspeeding and harsh manoeuvring of the aircraft at high speed.