Incident Overview
On July 9, 2013, at approximately 2000 mountain daylight time, a Stinson 108-3, registration N703C, experienced a total loss of engine power and subsequently landed in a field in Blackfoot, Idaho. The aircraft was registered to and operated by the non-certificated pilot under 14 Code of Federal Regulations Part 91. The pilot, the sole occupant, was not injured; the airplane sustained substantial damage. The flight, local and personal, departed from McCarley Field Airport in Blackfoot at about 1945. Visual meteorological conditions prevailed, and no flight plan had been filed.
Pilot Account
The pilot stated that he departed for a short practice flight with approximately 8 to 9 gallons of fuel onboard. After about 15 minutes airborne, at an altitude of roughly 1,000 feet above ground level, he heard a knocking sound from the engine compartment. Shortly thereafter, engine power reduced by about 50 percent, and the airplane began to lose altitude. The pilot switched the fuel selector to the other fuel tank and selected a wheat field for a forced landing. During the landing roll, the airplane flipped over and came to rest inverted. The pilot estimated that he had about 4 to 5 gallons of fuel remaining at the time of the accident.
Post-Accident Examination
A Federal Aviation Administration certificated airframe and powerplant mechanic conducted a post-accident examination. At the accident site, the right fuel cap remained secure on the wing, and the right fuel tank was not breached. An eight-inch diameter area of blight and fuel-soaked soil was observed near the right wing. Upon recovery, 30 ounces of fuel were drained from the right tank. The left fuel cap was found in the soil adjacent to the wing; the left tank was not breached. A 4.5-foot diameter area of blight and fuel-soaked soil was present near the left wing. The mechanic obtained 10 ounces of auto fuel and 2 tablespoons of water from the left tank. Disassembly of the gascolator revealed the bowl was about half full of cloudy fuel, and the screen was free of debris.
Fuel System and Selector
The fuel selector valve rotated freely, although the mechanic noted that the detents could not be felt—only a click was audible. No evidence of mechanical malfunctions or failures that would have precluded normal operation was found.
Aircraft Fuel System Description
The airplane's fuel system was designed to supply the engine via two aluminum fuel tanks located in the left and right wings. Each tank holds 25 gallons, with 2 gallons unusable in level flight conditions. A strainer was located in the outlet of each tank. Fuel was gravity-fed to the fuel selector valve, which had positions labeled "23 GAL L," "23 GAL R," and "FUEL OFF" on the bottom. The selector handle was shorter on the indicating/pointing side. From the selector, fuel flowed to another strainer and then to the engine's carburetor.