What happened
A commercial certificated pilot was performing a cross-country maintenance test flight following a recent engine overhaul. The engine had been recently installed by company maintenance personnel, and the flight was intended to accumulate flight hours on the new installation. During the flight, the pilot observed that the engine oil pressure was approximately 50 psi. After making slight adjustments to the engine RPM and manifold pressure settings, the oil pressure rose rapidly to the top of its operating range. While engine cylinder and oil temperature readings remained unchanged, the engine subsequently lost power.
The pilot attempted to restore power by switching the fuel selector from the left tank to the right tank and activating the engine boost pump, but power was not restored. The pilot then switched the selector back to the left tank. Although the engine sounded as if it were firing on all cylinders, it would only maintain an idle. The pilot noted that the engine transitioned from full power to idle immediately without any sputtering or coughing, though he could not confirm if the left fuel tank had been completely exhausted.
The flight ended in a forced landing where the aircraft collided with trees. There were no fatalities reported in this accident.
The investigation
An FAA inspector examined the aircraft at the accident scene. The investigation revealed that the left fuel tank was empty, while the right fuel tank contained approximately 15 gallons of fuel. No evidence of fuel leaks was found, and the engine and propeller controls were properly attached. During testing, the inspector noted that the engine could not be operated above idle due to broken engine mounts, though throttle movement did cause an increase in RPM. Additionally, the operator had sent the engine to a maintenance facility where it successfully operated at full power on an engine test stand.