NTSB Identification: CEN11LA404
14 CFR Part 137: Agricultural
Accident occurred Thursday, June 16, 2011 in Athleimer, AR
Probable Cause Approval Date: 09/05/2013
Aircraft: AYRES CORPORATION S2R-T34, registration: N30902
Injuries: 1 Minor.

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 had just started his first pass spraying fertilizer when the turboprop engine “exploded” and the propeller suddenly stopped. He saw flames around the cowling and soot and pieces of metal were exiting the exhaust stack. The pilot made a forced landing to a field, which resulted in the landing gear being torn from the airplane. The pilot was able to exit before the airplane was completely consumed by fire. A teardown examination of the engine revealed a failure in the first stage planetary gearset of the propeller reduction gearbox. All the gear teeth of the sun gear were ground down as far as the gear tooth roots, and the three meshing planetary gear teeth were battered and mutilated with only about 2/3 of the gear teeth height remaining. Review of the documentation of the last repair revealed that the gearset was a used replacement from another engine, contrary to manufacturer guidance, which states that first stage planetary gears should be replaced with a new gearset. The shop that sold the used gearset had misrepresented it as being zero-timed. The hours accumulated on the used gearset were beyond the manufacturer’s recommended time between overhaul.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

Failure of the first stage planetary gearset in the propeller reduction gearbox, which resulted in catastrophic engine failure. Contributing to the failure was the misrepresentation of the gearset being zero-timed by the company that sold the gearset to the operator. Also contributing was the total accumulated hours on the used gearset, which were beyond the manufacturer's recommended time between overhaul.

Full narrative available

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