Accident Overview
The pilot reported that during the takeoff roll for an aerial application flight, a loud pop was heard and sparks were observed near the engine compartment. With insufficient runway remaining to stop, the aircraft departed the end of the runway and collided with a ditch.
Engine Examination
Post-accident examination of the engine assembly revealed a total failure of several compressor turbine blades. Metallurgical analysis of the failed blades showed voiding and grain separation toward the tip grain boundary along a reaction zone, indicative of creep propagation. A comparison of the microstructure at the airfoil tip revealed a significant difference, with the tip appearing to be solutioned. According to the original equipment maintenance manual, blade tips that are solutioned indicate an over temperature event. The manual specifies that if the inter-turbine temperature exceeds 875 degrees Celsius for 2 seconds, the engine must be returned to an overhaul facility.
Determination of Over Temperature Cause
It could not be determined when or who exceeded the over temperature limit.