NTSB Factual Report

On July 17, 2003, at 1230 central daylight time, an Ayres Corporation S2R-G10, N3299A, operated by Peterson Aerial Spraying, was substantially damaged when it impacted trees during a forced landing 5 miles south of Staples Municipal Airport (SAZ), Staples, Minnesota. During an aerial application, the engine lost oil pressure, and the pilot then attempted to return to SAZ. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 137 flight was operating without a flight plan. The pilot reported no injuries. The flight departed Clarissa Municipal Airport, Clarissa, Minnesota, at 1215.

The pilot stated that during an aerial application, the low oil pressure light illuminated, and the oil pressure gauge was indicating below red line. He then started a climb towards the nearest airport. About five seconds later, the propeller went into feather and the engine stopped. He stated that he had never landed with a feathered propeller and when he attempted to land in a clearing, he floated across it and into trees at the far end.

The turboprop engine (TPE331-10-511M; serial number P36356C) was removed and shipped to Honeywell Engines, Systems and Services, Phoenix, Arizona, where it underwent disassembly and examination under the supervision of the Federal Aviation Administration (FAA). The examination revealed a separation through the oil jet flange consistent with high cycle fatigue that initiated at several locations along the flange surface. No tool marks were noted in the area. The oil jet flange material was consistent with the specified aluminum alloy.

The FAA and Honeywell were parties to the investigation.

NTSB Probable Cause

The fatigue fracture of the oil jet flange resulting in a total engine failure during the aerial application.