N873X – STEEN SKYBOLT – 2024-05-26 NTSB Accident Report

On May 25, 2024, about 1715 Pacific daylight time, an experimental amateur-built Steen Skybolt airplane, N873X, was substantially damaged when it was involved in an accident near Santa Maria, California. The pilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot reported that he had recently purchased the airplane and was relocating it from Lodi, California, to his home airport in Santa Maria, California (202 nautical miles). Before departure, the pilot topped off the main fuel tank (29 gallons total, 1 gallon unusable) and verified that the fuel selector was selected to the main tank.

For the 1.5-hour flight to Santa Maria, the pilot calculated a planned fuel burn of 12 gallons per hour based on previous flights, which would result in about 7.7 gallons of usable fuel remaining upon arrival. The pilot stated that after he climbed to 5,500 ft mean sea level, he reduced power to a setting of 23 inches of manifold pressure and 2,300 rpm, and then leaned to peak EGT, and then enriched the mixture by 50°.

The arrival and prelanding checks were described as normal. The pilot chose to extend the downwind leg to allow for a longer, stabilized approach. During the descent, while making a left base turn with 10–20° of bank and reducing engine power, the engine sputtered twice and then lost all power. The pilot completed the engine failure checklist but was unable to restore engine power.

Unable to reach the runway, the pilot initiated an emergency landing in a nearby field. While on final approach about 300 ft agl, the pilot observed rising terrain and lowered the nose to increase airspeed and clear a hill. Although the airplane cleared the terrain, it was unable to clear adjacent high-tension power lines. The pilot pitched the nose up, clearing the propeller and main landing gear; however, the tailwheel contacted a power line, resulting in a rapid deceleration and a nose-down pitch attitude of about 70–80°. The tailwheel subsequently released from the power line, and the airplane descended through a large tree, impacting terrain on a private gravel road. The airplane came to rest inverted, resulting in substantial damage to the upper left wing and horizontal stabilizer.

The pilot reported that the airplane remained inverted and leaked fuel from the main tank fuel cap for about three to four hours until it was turned upright by the recovery company.

A postaccident examination of the engine was performed on the recovered airplane. The two top engine mounts were fractured consistent with impact damage. The mechanical fuel pump and the left magneto were separated from their mounts consistent with impact damage. The upper spark plugs indicated between normal and worn-out normal with some black deposits within the electrode area. After removing the damaged propeller, the crankshaft was free and easy to rotate in both directions using a hand tool. Thumb compression was observed in proper firing order on all six cylinders. Mechanical continuity was established throughout the rotating/reciprocating group and accessory section during hand rotation of the crankshaft.

The valvetrain was observed to function normally during hand rotation of the crankshaft. Normal lift action was observed at each rocker arm. The gas path and combustion signatures observed at the spark plugs and exhaust system components displayed coloration consistent with normal operation. No oil residue was observed in the exhaust system gas path. Engine control continuity was established. The fractured fuel pump actuator arm moved normally on its cam when the engine was rotated. The right magneto timing was within normal range. Exhaust manifolds were free of obstruction. After opening the oil filter, no particulates were found. No pre-accident mechanical malfunctions were found with the engine during the examination that would have precluded normal operation.

The fuel selector lever was found in the On position. Fuel system continuity was established from the fuel tank 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.

The Bendix pressure carburetor was removed and tested, and it functioned normally, responding appropriately to airflow changes.

The previous owner stated that he 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.

A calculated fuel burn for the reported cruise power setting of 23 inches of manifold pressure and 2,300 rpm, utilizing Lycoming’s performance chart, at sea level, with a full rich mixture, equated to an approximate fuel burn of 15.8 gallons per hour. 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.