On August 20, 2002, an Air Tractor AT-502B (registration N6146G) was involved in an aviation accident near Rigby, ID. Investigators recorded the probable cause as: The failure of one or more compressor turbine blades resulting in a shutdown of the engine during initial climb resulting in a forced landing. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During climb, an Air Tractor AT-502B experienced an engine failure. The pilot performed a forced landing, during which the aircraft struck a ditch, causing landing gear separation.
Accident Details
The pilot reported that engine start and takeoff power application were normal. While climbing through approximately 100 feet, a loud bang was heard, and sparks and flames were observed exiting the engine exhaust ports. The pilot transitioned to a power-off forced landing. During the landing rollout, the aircraft encountered a ditch, resulting in separation of the main landing gear.
Engine Examination
Post-crash examination revealed extensive damage to the compressor turbine disk blades and erosive burning damage to the vane ring vanes situated immediately upstream of the compressor turbine disk. The engine, a Pratt & Whitney PT6A-34 turboshaft engine (22 years old), had 7,070 hours since new. An undocumented overhaul had been performed 5,820 hours prior to the accident. The last hot section inspection recorded in the engine log was conducted 2,871 hours before the accident, and the last logged inspection was a 100-hour inspection performed 324 hours and eight months prior to the event.