COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 106 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES General Electric Turbine Engines - CF6 Series AD/CF6/18 High Pressure Turbine Inspection and Improved Shroud Cooling Applicability: All model CF6-80C2, A5, B6, B6 F and DIF. Requirement: Carry out the technical requirements of FAA AD 91-05-21 Amdt 39-6900. 6/91 Compliance: As detailed in Requirement Document with a revised effective date of 13 June 1991. Background: The AD introduces a borescope inspection program to detect high pressure turbine (HPT) stage 1 shroud and blade distress. Also, it requires installation of improved HPT hardware which increases the cooling to the HPT stage 1 shroud. The AD is prompted by one HPT failure which resulted in aircraft damage.