NTSB Factual Report

On August 11, 2001, approximately 0720 Pacific daylight time, a Grumman G-164B "Agcat" spray plane, N6774Q, registered to and being flown by a commercial pilot, was substantially damaged when the aircraft nosed over during an emergency landing following a total loss of power on takeoff at a private airstrip southeast of Quincy, Washington. The pilot was uninjured. Visual meteorological conditions existed and no flight plan had been filed. The flight, which was intended for aerial application, was operated under 14 CFR 137.

The pilot/owner reported that just as he broke ground on takeoff the engine bogged down and an oil spray appeared on the windscreen. He dumped the chemical load and continued straight ahead into an agricultural field during which the aircraft came to rest inverted (refer to photograph 1). The engine had come to a complete stop before the aircraft nosed over.

The pilot also reported that a post-crash examination of the newly rebuilt Pratt & Whitney 1340 radial engine revealed substantial metal in the oil filter and on the magnetic sump plug. He stated that the engine had approximately 250 hours since rebuild, which was accomplished by a company located in Winnipeg, Manitoba, Canada.

The engine was disassembled and examined at the facilities of Aero Recip (Canada Ltd.) with oversight provided by personnel from the Winnipeg office of the Canadian Transportation Safety Board. The disassembly revealed evidence of impeller rub on the rear impeller case. The impeller collector case displayed severe abrasion and likewise, the impeller displayed severe damage. The impeller shaft was bent, as was the ring carrier, and both showed evidence of overheating. The impeller shaft cage was damaged and the bearing material was smeared over the oil holes. However, all oil passages leading to the impeller bearings were found to be free and clear of obstructions (refer to attached AMO Report No. 45-89).

The impeller and impeller collector case were sent to the Engineering Branch Laboratory of the Canadian Transportation Safety Board for further examination. The report stated that although the impeller blades and impeller fragments examined revealed no signs of any progressive failure mechanism, the degree of damage was to such an extent as to prevent a conclusive determination of the sequence of events (refer to attached report LP077/2001).

NTSB Probable Cause

The failure of the impeller assembly as a consequence of impeller rub and binding within the impeller collector case for undetermined reasons.