Incident Overview
A Beechcraft Bonanza C35 sustained substantial damage during a forced landing following a loss of engine power. The aircraft had just undergone an engine overhaul and reinstallation. After a successful ground run, a flight test was conducted with a pilot and an aircraft mechanic on board.
Flight Details
The flight departed with 20 gallons of fuel in the right main tank, 5 gallons in the left main tank, and 10 gallons in an auxiliary tank. The pilot selected the right fuel tank for takeoff and climb, reaching 8,500 feet mean sea level while circling the airport to evaluate engine performance. The pilot noted that the new fuel pump was producing approximately 15 psi, compared to the previous pump's 9 psi.
Incident Sequence
After about an hour of flight, the pilot initiated a descent to land, keeping the fuel selector on the right tank. While on final approach, he added power, but the engine did not respond. He was unable to restore engine power before the aircraft impacted the ground.
Post-Accident Inspection
An examination of the airplane revealed 6 gallons of fuel in the left tank and 2.5 gallons in the right tank. Each wing fuel tank held 20 gallons total, with 17 gallons usable. No airframe or engine anomalies were found. The engine was subsequently removed and run on a test stand, where it started and operated normally.
Pilot's Assessment
The pilot theorized that the increased fuel pump pressure caused an accelerated transfer of fuel from the right tank to the left tank, leading to fuel starvation in the selected tank. He stated, "I think what happened was that the increased fuel pump pressure transferred the fuel from the right tank into the left tank at an accelerated rate, and I had no idea that I was getting that close to empty."
Aircraft Manual Guidance
The Beechcraft Bonanza C35 Pilot's Operating Handbook (POH) specifies that takeoffs should be made using the left main tank and landings using the main tank that is more nearly full. It also notes that the pressure-type carburetor returns about 3 gallons per hour of excess fuel to the left main cell regardless of the tank selected.