COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 106 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Allison Turbine Engines - 250 Series AD/AL 250/71 Turbine Splined Adapter Locknut Torque 12/86 TX Applicability: Model 250-C28 and -C30 series and turbines with serial numbers CAT 70001 through 70802 and 70804: CAT 28001 through 28046: and CAT 90001 through 95436 and 95438, and those turbines which have not been assembled or had turbine splined adapter locknut torque checked in accordance with: CEB-A-72-2132/3146; THO- 2639W-RFR-85 dated 7 February 1985; C28 Overhaul Manual Temporary Revision 72-7 dated 22 January 1986; C30 Overhaul Manual Revision 1 dated 1 July 1985, or CSL-2071/3073 dated 1 June 1985. Requirement: Inspect the gas generator turbine splined adapter locknut torque in accordance with Allison CEB-A-72-2132/3146 dated 1 October 1985 or approved equivalent. FAA Emergency Priority Letter AD 86-20-13 refers. Compliance: Unless already accomplished, within 5 hours' time in service after 27 October 1986 but not later than 31 October 1986. Background: Allison CSL-A-2084/3087 dated 10 September 1986 advises a recent contained C30 turbine wheel failure. Excessive wear and/or fretting of the splined connection between turbine splined adapter and turbine to compressor shaft can result from insufficient torque on the splined adapter locknut. This can lead to disconnect, overspeed and failure of the gas generator turbine. This Directive is issued to prevent excessive wear and/or fretting occurring due to improper torque of the splined adapter locknut.