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 250/58 Amdt 2 Gearbox Assembly - PTO Helical Gearshaft Assembly - Replacement 9/84 Applicability: All Model 250-C18, C20, C20B, C20F, B15G, B17, B17B, and B17C, engines with exceptions as listed in the requirement document. Requirement: Allison 250-C18, C18A, C18B, C18C Allison 250-C20, C20B, C20F Allison 250-B15G Allison 250-B17, B17B, B17C : CEB-203 : CEB-1150 : TP CEB-71 : TP CEB-1126 Rev. 7 Rev. 7 Rev. 7 Rev. 7 Compliance: In accordance with the Requirement Document Para E. Background: This Directive is amended to reflect the manufacturers Rev. 7 changes to the Requirement Documents Para 1.E Compliance Statement; sub-para 3 which requires the immediate replacement of superseded part numbered PTO shaft in the event of future shockload or sudden stoppage as defined in Para 3.1 and 3.2.