COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 106 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES AlliedSignal (Lycoming) Turbine Engines - ALF502 and LF507 Series AD/ALF/13 Third Stage Compressor Disc Inspection 13/93 Applicability: All Textron-Lycoming ALF 502 L and R series engines incorporating 3rd stage compressor discs as detailed the Requirement documents. Requirement: Inspect affected 3rd stage compressor discs in accordance with Textron-Lycoming Service Bulletins ALF 502L 72-259 or ALF 502R 72-259 as applicable. Note: FAA AD 93-10-07 also refers. Compliance: Effective 1 January 1994. As detailed in the Requirement Documents. Background: A number of 3rd stage compressor discs have been identified where the Sermetel W protective coating may be defective due to improper surface preparation. This can lead to lack of adhesion and subsequent flaking of the coating. Degraded coating can result in corrosion of the disc and potential disc failure.