COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 106 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Pratt and Whitney Turbine Engines - PW4000 Series AD/PW4000/2 2nd Stage HPT Rotating Airseal 1/99 Applicability: PW4000 series engines. Requirement: 1. Inspect 2nd stage high pressure turbine rotating airseals in accordance with Pratt and Whitney Alert Service Bulletins, PW4ENG A72-628, Rev. 1, and PW4G-100- A72-80, Rev. 1, as applicable. 2. Modify 2nd stage ring segments and vane clusters, and install improved 2nd stage high pressure turbine rotating seals in accordance with Pratt and Whitney Service Bulletins PW4ENG 72-636, PW4ENG 72-637, PW4G-10- 72-93, and PW4G-100- 72-94, as applicable. Incorporation of these modifications and installation of an improved 2nd stage HPT rotating airseal constitutes terminating action for Requirement 1 of this Directive. Note: FAA AD 98-19-03 also refers. Compliance: 1. At each occasion the HPT is disassembled after the effective date of this Directive. 2. Within 6 years after the effective date of this Directive. This Airworthiness Directive becomes effective on 28 January 1999. Background: This Directive is prompted by reports of 2nd stage HPT rotating airseal cracking which could result in an uncontained engine failure and damage to an aircraft.