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/PW4000/4 Low Pressure Turbine Stage 4 Disk 10/99 Applicability: PW4000 series engines with a Low Pressure Turbine (LPT) Stage 4 disk as specified in FAA AD 99-15-01. Requirement: Replace affected LPT Stage 4 Disks in accordance with the technical requirements of FAA AD 99-15-01. Note: Pratt and Whitney Service Bulletins PW4ENG 72-657 and PW4G 100-72-105 also refer. Compliance: At periods detailed in the Requirement document. This Airworthiness Directive becomes effective on 7 October 1999. Background: This Directive is prompted by advice that a change in cooling hole geometry on affected LPT disks results in a reduction in cooling air flow to the disk and higher stresses. Higher than normal stress could result in an uncontained disk failure.