Amateur-built SKYBOLT N873X accident near Santa Maria, California

Probable cause

A total loss of engine power during approach for reasons that could not be determined.

NTSB analysis

The pilot had just purchased the airplane before departing on the cross-country flight. He conducted preflight fuel planning based on the airplane’s total fuel capacity and the fuel consumption rate he had calculated (28 usable gallons at 12 gallons per hour, respectively). The pilot filled the main tank for the flight and determined a fuel stop was not required.

The pilot stated that after departure, and upon reaching his intended cruise altitude, he reduced power to 2,300 rpm, 23 inches of manifold pressure, and leaned the mixture to peak EGT followed by enriching 50°. Upon arrival to the destination airport, the pilot chose to extend the downwind leg to allow for a longer, stabilized approach. While turning left base to the runway, the engine sputtered two times and then lost all power. While troubleshooting, the pilot was unsuccessful at restarting the engine and initiated an emergency landing to a nearby field. At 300 ft above ground level (agl), he realized that the terrain was steeper than he originally thought. The pilot maneuvered the airplane to gain airspeed to overfly a hill in his flightpath. As the airplane passed over the hill, the pilot observed a set of high-tension power lines. He attempted to fly over the power lines; however, the tailwheel contacted a power line and the airplane subsequently pitched down, falling through trees, impacting terrain, and coming to rest inverted on a road.

The previous owner of the airplane used the airplane to fly aerobatics and rarely flew the airplane over 30 minutes at a time before refueling. He typically operated the airplane with 25 gallons of fuel on these flights, and he estimated the engine’s fuel consumption was about 16 gallons per hour at a full-throttle power setting. When discussing the airplane relocation flight with the accident pilot, he suggested flying at a reduced airspeed, flying straight and level, and making a fueling stop en route.

The pilot stated that the airplane remained inverted during the three to four hours it took to recover the airplane from the accident site. During that time, fuel leaked out of the main tank filler cap.

The fuel selector lever was found in the On position. Continuity of the fuel system was established from the main fuel tank throughout the system to the pressure carburetor. Observing fuel in the fuel tank, the airplane was positioned in a level flight attitude, and the electric fuel pump was activated; initially no fuel pressure was observed. After about 15 seconds, the pump noise changed consistent with pump priming. Fuel was then observed dripping from the pressure carburetor, with the cockpit fuel pressure gauge indicating pressure within the green arc.

Examination of the recovered engine revealed no pre-accident mechanical malfunction or failure that would have precluded normal operation. Although it is possible that the loss of engine power may have been fuel-related, it could not be substantiated with the available evidence. A calculated fuel burn for the reported cruise power setting with a full rich mixture, equated to an approximate fuel burn of 15.8 gallons per hour for the 1.5 hour flight. The calculated fuel burn in a full rich condition would have resulted in about 3 gallons of useable fuel remaining. In a leaned configuration, it’s likely there could have been up to 10 gallons of fuel remaining.

Text from the NTSB. Open the NTSB docket for WPR24LA160 for the full record.