COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 106 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Pratt and Whitney Turbine Engines - JT9D Series AD/JT9D/16 HPC Variable Stator Synchronising Ring Runner Clearance Applicability: JT9D-7R4 D/D1/E/E1/E4 and H1 series engines. 2/87 TX Requirement: Fit synchronising ring runners having specified clearances to comply at minimum with the requirements of FAA Emergency Telex Airworthiness Directive/TAD/number T86-25-51 dated 12 December 1986. (Revised operating procedures are involved if only minimum levels of compliance are incorporated). Compliance: To be incorporated into at least one engine per aircraft before further flight after 25 December 1986 and into all engines by 31 December 1987. Background: The FAA has determined that clearance between the high pressure compressor case and the variable stator vane synchronising ring runners decreases during operation at take off power and could cause temporary binding in the system during power reduction. An engine deceleration during the take off/climb period can cause the stator vanes to remain open reducing the available surge margin.