Incident Overview
During takeoff climb, the pilot heard a loud "thunk" and experienced a loss of engine power. The pilot moved the power lever from full forward to full aft without restoring power, resulting in a forced landing onto a road and scrub brush.
Engine Examination
Post-accident examination of the Pratt & Whitney Canada PT6A-114A engine found that a section of the compressor turbine (CT) vane's outer rim had liberated. This liberated material damaged the turbine blades downstream, leading to the total power loss. Metallurgical analysis by the manufacturer identified fatigue on the fracture surface of the outer rim, with signs of oxidation in some areas, indicating the crack had existed for some time.
Maintenance Records
The operator's records showed the engine was approved for an extension beyond the standard 3,600-hour overhaul period to 5,100 hours. At the time of the accident, the engine had accumulated 4,461.3 hours. The turbine section (hot section) had a recommended overhaul period of 1,800 hours; however, the operator elected to use an engine trend monitoring program per a manufacturer service bulletin. Many errors were noted in the operator's manually recorded data. Nevertheless, even correctly recorded data likely would not have detected the fatigue cracking.
Manufacturer Actions
Following a similar investigation, the manufacturer issued Service Information Letter PT6A116 on January 27, 2003, reminding operators to perform borescope inspections of the CT vane during routine fuel nozzle maintenance, as recommended in the maintenance manual. Review of the accident engine's maintenance records showed no evidence that such an inspection had been conducted during fuel nozzle checks.
Probable Cause
The fatigue failure of the compressor turbine stator vane, the liberation of vane material into the compressor turbine, and the total loss of engine power were causal. Also causal was the operator's failure to inspect the compressor turbine vane during fuel nozzle checks.