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/TB20/2 Landing Gear Micro Switches - Adjustment 3/85 Applicability: All model TB20 with S/Nos up to and including 459. Requirement: Adjust the undercarriage micro switches according to the requirements contained in Socata TB SB No 23. Note: French AD 85-4(A) refers. Compliance: Within 50 hours time in service after 31 March 1985. Background: Compliance with this Directive will minimise the possibility of inadvertent undercarriage collapse.