On June 27, 2022, about 1002 mountain daylight time, an experimental amateur-built Van’s RV-9A airplane, N12VV, was substantially damaged when it was involved in an accident near Missoula, Montana. The pilot was seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot (and builder of the accident airplane), he was performing flight tests on his airplane to break in the engine. The pilot reported that he completed one test flight on the morning of the accident and landed about 0800 to refuel the airplane. He then departed with the fuel selector positioned on the right fuel tank. The right fuel tank contained16 gallons of fuel; 8 gallons of fuel were in the left tank. Data retrieved from an onboard recording device showed that the airplane departed runway 29 at 0850. The pilot flew the airplane in a racetrack style pattern from the southeast to northwest in an area about 2 nautical miles (nm) west of his departure airport for about 1 hour 15 minutes. According to the parametric data, at 1000:10 the fuel flow became increasingly erratic with two spikes indicating a fuel consumption of about 42 gph. During this time, the engine speed, exhaust gas temperatures, and cylinder head temperatures decreased over time. The pilot contacted air traffic control to inform them that his engine was “surging” and was “probably about to quit.” The controller then cleared the pilot to land on runway 8. After the engine quit the pilot switched fuel tanks from the right tank to the left tank and the engine restarted for about 2 seconds before it quit again. An airport surveillance video showed the airplane descending from a low altitude as it approached the airport from the northwest. While passing near the approach end of runway 8, the airplane made a steep left turn from an estimated altitude of about 30 ft above ground level and descended rapidly towards the ground and impacted terrain, which resulted in substantial damage to the left wing. The airport manager stated that the wreckage came to rest between runway 12/30 and taxiway alpha between midfield and the approach end of runway 30. The wreckage was located about 0.5 nm east of the approach end of runway 8. Wreckage examination Postaccident examination of the airplane and engine did not reveal any preimpact mechanical anomalies. The fuel system was traced from each wing tank to the carburetor at the engine through the fuel selector, which rotated normally and was unobstructed. The fuel lines that had not been damaged from impact or removed to transport the airplane were secure. Mechanical continuity was established throughout the rotating group, valvetrain, and accessory section as the crankshaft was manually rotated at the propeller by hand. Thumb compression was achieved at all four cylinders and the valves displayed normal lift when the crankshaft was rotated. Examination of the cylinders’ combustion chamber interior components using a lighted borescope revealed normal piston face and valve signatures and no indications of catastrophic engine failure. The engine-driven fuel pump functioned normally when tested by hand. Fuel Consumption Data retrieved from a Garmin G3X onboard recording unit displayed the fuel quantities as 18 gallons in the right tank and 18 gallons in the left tank (totaling 36 gallons) from 0837 to 0849. At 0849, about when the engine was advanced to full power, the fuel quantities changed to 2 gallons in the left fuel tank and 13 gallons in the right fuel tank. These quantities were displayed for the remainder of the flight. The fuel flow advanced to about 10 gph during takeoff and remained between 10-14 gph until about 1000, at which time the fuel flow became erratic showing a minimum of 2 gph and a maximum of 42 gph at 1001:19. One second later, the engine speed began to reduce from 2,240 rpm to idle power and then 100 rpm. According to the engine manual for an O-360-A1A, which is comparable to the engine that was installed on the accident airplane and had the same compression ratio, the fuel consumption is 9.5 gph at 65% power, 10.5 gph at 75% power, and 14.9 gph at 100% power. Using the recorded engine data, an average fuel consumption of 12 gph would have resulted in a total fuel burn of about 14 gallons. The pilot reported that he was using 10.5 gph to determine the engine’s fuel consumption for the flight and added that he did not activate the electric fuel pump after the engine quit. At 10.5 gph, the engine would have consumed a total of about 12.25 gallons in the airplane’s 70 minutes of flight. According to the pilot, he had not yet determined the airplane’s unusable fuel quantity, but assumed it was about 1 gallon. The pilot also noted that he was operating at higher power settings to break in the engine during the accident flight.