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/CF6/21 Eddy Current Inspection of High Pressure Turbine Thermal Shields Applicability: CF6-45/-50 series engines. 11/91 Requirement: Action in accordance with the Technical Requirements of FAA AD 91-15-16, Amendment 39-7080. Note: General Electric Service Bulletin 72-879 Revision 6 refers. Compliance: As specified in the Requirement Document with an effective date of 28 November 1991. Background: Four HPT stage one discs have been found cracked during inspection. The condition, if not corrected could result in uncontained engine failure.