What happened
On November 29, 2012, a Cessna 208B, registration N1324G, was conducting a scheduled night cargo flight from Guymon Municipal Airport (GUY) to West Woodward Airport. While climbing through approximately 7,000 feet, the pilot reported a loud bang followed by the propeller spooling down toward the feather position and coming to a stop.
The pilot attempted both an air-start and an electric start, but neither was successful. During the subsequent forced landing approach toward a two-lane highway, the aircraft struck a power line. The airplane then made a hard landing, exited the left side of the highway, and struck a power pole, which caused damage to the left wing. The pilot, who was the sole occupant, sustained one minor injury and was not killed.
The investigation
Post-accident examination of the Pratt & Whitney PT6A-114A engine revealed that the outer half-span of all power turbine blades were missing. Some power turbine blades showed evidence of melting and sequential fracturing. The compressor turbine (CT) blades exhibited rounded, burned tips and fractured trailing edges, which investigators noted was consistent with hard body impact.
Detailed examination of the engine in Quebec, Canada, determined that one compressor turbine blade (position No. 25) had fractured near its root. This specific blade displayed a fatigue fracture that initiated at the trailing edge and progressed forward. The failure of this blade released debris into the engine path, which then impacted adjacent blades and downstream components, leading to the total loss of engine power. While the exact initiation source of the fatigue crack could not be determined due to secondary damage, the investigation noted that the engine was equipped with older directionally solidified blades rather than the newer single crystal blades introduced via service bulletin SB1669.