COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Fokker F27 Series Aeroplanes AD/F27/90 Amdt 1 Pneumatic Isolating Valves - Inspection 7/77 Applicability: All models fitted with pneumatic isolating valves, Dunlop Aviation Division P/N ACM 17892 or ACM 26214. Requirement: Inspect using a method approved by the Secretary, pneumatic isolating valves, Dunlops Aviation Division P/N ACM 17892 or ACM 26214, for presence of cracks around internal circumference of body, P/N ACM 16724, ACO 22631 or ACM 26573 in area of undercut in main body chamber. Valve bodies showing crack indications extending through more than one third of the wall thickness must be replaced before further flight. Compliance: Within 250 hours time in service after 31 March 1977 and thereafter at intervals not exceeding 2400 hours time in service.