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/9 Engine Centre Section 9/90 Applicability: Viper Mk 601-22 and Viper Mk 520, 521 and 522 engines. Requirement: Inspect engine compressor casing/centre section joint flange in accordance with and as applicable: Rolls Royce Viper Mk 601-22 Service Bulletin No 72-A173; or Rolls Royce Viper Mk 520, 521, and 522 Service Bulletin No 72-A388. Compliance: (1) Engines in service - Prior to 6 August 1990. (2) Uninstalled engines - Prior to installation in an aircraft. Background: Investigation of an engine established that the compressor casing/centre section joint had parted at the top, causing heavy bending loads on the turbine mainshaft causing spline failure. Parting of the compressor casing/centre section has been attributed to thermal stress pulling fastener inserts from the centre section.