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/TB20/19 Oil Cooler Inlet and Outlet Elbows 1/91 Applicability: All model TB20 and TB21 aircraft. Requirement: Action in accordance with Socata Service Bulletin NR 50-1. Note: DGAC AD 90-143(A) refers. Compliance: Prior to 31 January 1991. Background: Leakage from the oil cooler inlet and outlet elbow has resulted in total engine oil loss.