COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Aerospatiale (Socata) TB20 (Trinidad) Series Aeroplanes AD/TB20/25 Autopilot Master Switch 2/92 Applicability: All TB20 and TB21 with S/No's 275 thru 1222 fitted with one of the following options: 668, G668, 669, G669, 670 or G670. Requirement: Action in accordance with Aerospatiale SOCATA Service Bulletin No 60. Note: DGAC AD 91-145A refers. Compliance: Prior to the next Maintenance Release after 28 February 1992. Background: To reduce the risk of a short circuit at the "A/P Master" switch.