NTSB Identification: ATL02LA060.
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Accident occurred Tuesday, March 05, 2002 in Schlater, MS
Probable Cause Approval Date: 11/25/2003
Aircraft: Air Tractor AT-502, registration: N9185F
Injuries: 1 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The pilot stated he was on takeoff roll to conduct aerial application flight. Just before rotation he heard a loud pop and observed sparks in the vicinity of the engine compartment. There was insufficient runway remaining to stop the airplane. The airplane went off the end of the runway and collided with a ditch. Examination of the engine assembly revealed a total failure of several compressor turbine blades. Metallurgical examination of the compressor turbine blades revealed voiding and grain separation were observed toward the tip grain boundary along a reaction zone which is indicative of creep propagation. A comparison of the microstructure at the airfoil tip revealed a significant difference in the structure with the tip appearing to be solutioned. According to the original equipment maintenance manual blade tips that are solutioned is an indication of over temperature. if the inter-turbine temperature exceeds 875-degrees Celsius for 2 seconds the engine is required to be returned to an overhaul facility. It could not be determined when or who exceeded the over temperature limit.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: an unknown person at an unknown time exceeded the engine temperature limitations that resulted in the failure of compressor turbine and the subsequent loss of engine power during takeoff.
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