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 250/38 Idler Gearshafts - Replacement 10/79 Applicability: All 250-C28 and -C30 series models fitted with generator idler gearshaft P/N 6898980 or 6898591 and 77 tooth idler gearshaft P/N 6898652. Document: 1. Allison 250-C28 CEB No. 72-2003; or Allison 250-C30 CEB No. 72-3003; or 2. FAA AD 79-16-06 Amendment 39-3527 also refers. Compliance: 1. For 250-C28 engines: Prior to reaching 9000 cycles. 2. For 250-C30 engines: Prior to reaching 2000 cycles. 3. For engines which may have exceeded the maximum permissible number of cycle at the time of promulgation of this Directive 3 September 1979, within 50 cycles. Background: This Directive is issued to prevent sudden power loss due to accessory drive gearbox gearshaft failure.