COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Pilatus PC-12 Series Aeroplanes AD/PC-12/10 Fuel Storage - Vent Valve System 8/98 DM Applicability: Model PC-12 and PC-12/45 airplanes serial numbers 101 - 230 (incl). Requirement: Modify the fuel storage vent valve system by removing the inward vent valves and installing float valves and flame arrestors in accordance with the requirements of Pilatus Service Bulletin No.28-005 dated 04 May 1998. This Directive supersedes the requirements of AD/PC-12/9 Amdt 1 dated 4 December 1997 which will be cancelled. Note: FOCA AD HB 98-126 dated 15 May 1998 refers. Compliance: Within 60 days of the effective date of this AD. This airworthiness directive becomes effective on 27 May 1998. Background: Reports of abnormal automatic engagement of the fuel booster pumps during normal aircraft operations revealed that under certain circumstances the inward vent valves could fail shut. In this condition, operation of the boost pumps could cause permanent damage to the wing skin structure. Interim measures introduced under AD/PC-12/9 have since been found to be ineffective and a full modification of the fuel storage vent system has now been introduced. This Directive mandates the incorporation of the vent system modification and advises cancellation of AD/PC- 12/9 Amdt 1 dated 04 December 1997.