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-6/44 Horizontal Stabiliser Trim Actuator 12/99 TX Applicability: All PC-6 aircraft fitted with horizontal stabiliser trim actuator Pilatus P/N 978.73.18.101 or 978.73.18.102 or 978.73.18.103. Requirement: Inspect in accordance with the requirements of Pilatus Service Bulletin PC-6 No 178 dated 29 Sept 1999. Note: Swiss FOCA AD HB 99-507 refers. Compliance: For aircraft with more than 2000 landings or more than 500 hours TIS if the number of landings has not been recorded, inspect before further flight. For all other aircraft, inspect at the next 100 hourly inspection. This Airworthiness Directive becomes effective on 11 October 1999. Background: The Swiss Airworthiness Directive was written after the FOCA received a report of a lower lug of the electrical horizontal stabiliser trim actuator was found cracked and with a lug segment missing. The cause is suspected to be loosening of the staked bearing causing excessive wear and hence failure of the lower lug.