Accident Sequence
During a straight-in approach for landing, the pilot lost all power on the left engine. After switching to the left auxiliary tank, the engine did not restart. Approximately one minute later, all power was lost on the right engine. The pilot, believing the airplane was too low, did not attempt to switch to the right auxiliary tank and concentrated on making a forced landing on a city street directly ahead. After touchdown, the airplane's wing tip main fuel tanks collided with the front ends of two approaching school buses.
Fuel System Findings
Both main fuel tanks were ruptured in the accident and found empty. Only residual fuel was present in the lines. Investigators recovered 1 quart of fuel from the left auxiliary tank and 4 gallons from the right auxiliary tank. The exact fuel load at the time of the first departure that morning could not be determined; however, based on refueling records, the airplane would have had no less than 122 gallons.
Flight History
During the first leg of flight, a high cylinder head temperature reading led the pilot to make a precautionary landing at an airport just over halfway to the original destination. The total elapsed time at this landing was 1.3 hours. The pilot was then instructed to reposition the aircraft back to the point of departure. He relied on a preplanned flight plan provided by company dispatchers and did not recompute the fuel required for the return. No fuel was added before the return flight. The elapsed time on the return flight was 1.2 hours, for a total of 2.5 hours.
Fuel Management Details
The pilot reported that for both legs, he set a fuel flow of 18 gallons per hour per engine, which is above the red line gauge limit. Performance charts indicate the proper fuel flow setting was 13.35 gallons per hour per engine. Even at the higher fuel flow, investigators calculated that the airplane should have had a minimum of 12 gallons at the time of the accident; this fuel remains unaccounted for. The pilot stated that at some point during the two legs, he switched to the auxiliary tanks until the gauges read 2 and 5 gallons, then switched back to the main tanks. He could not specifically recall how long he had been flying on the mains when he switched tanks or on which leg the switch occurred.
Fuel System Characteristics
To avoid unwanted fuel venting overboard, a specific fuel tank use sequence must be followed. The engine-driven fuel pumps supply 50 percent more fuel than required to the metering valves for each engine, with the excess fuel returned to the corresponding main tank. The auxiliary tanks should not be selected until the main tanks have been used for at least 60 minutes, so that the mains have room for the returned excess flow from the auxiliary tanks.
Post-Accident Examination
No evidence of leakage or staining was found around the wing filler caps. Staining observed on the pavement around both buses could not be differentiated between fuel and a fire suppressive agent. After the accident, both engines were started and test run with no anomalies noted.