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/23 First Stage High Pressure Turbine Airseal 2/91 Applicability: JT9D-7R4D, -7R4D1, -7R4E, -7R4E1, -7R4E4, -7R4H1, -7R4G2, engines fitted with P/N 797576, 797576P48, 793707, 793707P48 first stage turbine airseals. Requirement: 1. Replace first stage high pressure turbine airseals as listed by serial number in PWA SB No JT9D-7R4-72-393 Rev 1, Para 2, Part A. 2. Inspect, first stage high pressure turbine airseals not listed by serial in PWA SB No JT9D-7R4-72-393 Rev 1, Para 2, Part A, in accordance with PWA SB No JT9D- 7R4-72-393 Rev 1, Para 2, Part B. Note: FAA AD 90-23-19 refers. Compliance: 1. At next engine shop visit regardless of planned maintenance action or reason for engine removal. 2. At next access to affected parts. Background: This Directive reflects advice of an uncontained JT9D-7R4H1 engine failure event. The failure was attributed to cracking of an Inconel-718 material airseal. Certain lower rated JT9D models may also be fitted with the same part number airseal. This Directive requires replacement or inspection of those airseals.