COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 106 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Rolls Royce Turbine Engines - Viper Series AD/VIPER/7 Oil Tank Drain Valve 7/90 Applicability: Viper Mk 601-22 engines. Requirement: Inspect oil tank drain valve assembly for leakage in accordance with Rolls Royce Viper Mk 601-22 Service Bulletin No 79-A4. Note: CAA (UK ) Airworthiness Directive 015-04-90 refers. Compliance: Effective 12 July 1990: (1) Engines in service - Prior to 20 July 1990. (2) Prior to installation in an aircraft. Background: Failure to detect oil leakage at the oil tank drain valve may result in total loss of oil pressure. Investigation of a total loss of oil pressure on a test flight following engine installation, revealed that the oil tank drain valve cap was not in position and the drain valve was stuck open allowing a rapid loss of oil tank contents.