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/TB20/4 Wing Drainage - Modification 4/85 DM Applicability: All model TB20 with S/Nos up to 433 and No 444. Requirement: Aerospatiale SOCATA TB SB No. 26. Compliance: Unless already accomplished, within the next 50 hours time in service after 8 March 1985. Background: The purpose of this modification is to provide proper drainage of the wing tip forward spar box.