Stinson 108-3 N703C accident near Blackfoot, Idaho

Probable cause

A partial loss of engine power during cruise flight for reasons that could not be determined because postaccident examination revealed no mechanical malfunctions or failures that would have precluded normal operation.

NTSB analysis

The noncertificated pilot reported that the airplane had been airborne for about 15 minutes and was about 1,000 feet above ground level when the engine experienced a partial loss of power and the airplane began to lose altitude. The pilot switched fuel tanks, but there was no change in power, so he then made a forced landing to a wheat field. During the landing, the airplane flipped over and then came to rest inverted. The pilot estimated that about 4 to 5 gallons of fuel were on board at the time of the accident. The right fuel tank was not breached, and it contained residual quantities of fuel below the usable limit. The left fuel tank was not breached; however, its fuel tank cap was displaced during the accident sequence, so an accurate assessment of the quantity of fuel in the left tank could not be determined; however, a 4.5-foot-diameter area of fuel-soaked soil was found near the left wing. Although water was found in the left tank, it may have entered through the displaced fuel tank cap. A postaccident engine examination revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation.

Text from the NTSB. Open the NTSB docket for WPR13LA320 for the full record.