FAA is looking for five Honeywell TPE331-10 and TPE331-11 first-stage turbine disks that may have a manufacturing defect. A defect in a sixth disk caused a fracture that led to an uncontained failure in May 2008. From today's airworthiness directive:
The fracture revealed a large melt-related oxide cluster inclusion in the web area of the disk, which occurred during the forging alloy melting process. The disk was produced from Waspaloy material, from Heat Lot 9-7121, which was melted by Special Metals in 1980. We have determined that five turbine disks that were next to the failed disk during the billet-forging process may also contain part of the same melt-related oxide cluster inclusion. This condition, if not corrected, could result in uncontained failure of the first stage turbine disks made from these billets and damage to the airplane.
The directive orders operators to remove from service P/Ns 3101520-1 and 3107079-1, serial numbers 2-03501-2299, 2-03501-2300, 2-03501-2301, 2-03501-2302, and 2-03501- 2304, within 25 flight hours or 25 cycles-in-service after the rule's Sept. 1 effective date.