COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES SAAB SF340 Series Aeroplanes AD/SF340/63 Airfoil De-Icing - Introduction of New Improved Check Valve 2/98 Applicability: SAAB 340B series aircraft serial number 240 through 430 (inclusive) with installed Check Valves BF Goodrich P/N 3D3511. Requirement: Install improved check valves in accordance with SAAB Service Bulletin 340-30- 080. Note: SAD N0. 1-120 refers. Compliance: Within six months of the effective date of this directive. This airworthiness directive becomes effective on 29 January 1998. Background: Operational tests on a SAAB 340 aircraft after engine change showed that the check valves had failed. Failed check valves may result in loss of airfoil de-ice system operation during single engine operation. A previous Service Bulletin introduced a design improvement (SAAB SB 340-30-069) and this was mandated at AD/SF340/56. Subsequent service experience has shown that this design was also defective. This AD cancels and supersedes AD/SF340/56 and gives instructions for the replacement or modification of check valves.