COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 106 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Pratt and Whitney Turbine Engines - JT8D Series AD/JT8D/4 Sixth Stage Compressor Disc and Blades 8/70 Applicability: All JT8D series engines incorporating sixth stage compressor discs P/Ns 483506, 494906 and 586906. Requirement: 1. Using a suitable borescope, inspect the rear of the sixth stage compressor blade dovetail roots and disc slots for any evidence of cracking. Any sixth stage compressor blade or disc found cracked shall be removed from service before further flight. Note: Pratt & Whitney SB No. 1133, Rev. 3 gives details of a modification for incorporating suitable borescope inspection ports in the compressor casing. or 2. AD/PW-T/27A. Compliance: At intervals not exceeding 500 hours time in service, after 31 August 1970.