What happened
During a scenic tour flight, the aircraft experienced a sudden loss of engine power. In an attempt to restore functionality, the pilot transitioned the fuel supply to the tank containing the most fuel; while this briefly restored power, the engine subsequently failed completely. During the descent, the propeller failed to windmill.
To avoid a more catastrophic impact, the pilot executed an off-airport landing within the difficult and rugged landscape of the Grand Canyon. The impact resulted in the total destruction of the aircraft and left all three occupants with serious injuries.
Findings
Post-accident inspections of the engine components identified that the crankshaft had undergone a fracture. A detailed examination of the break site confirmed that the failure was caused by subsurface metal fatigue. The difficulty of the forced landing was further compounded by the mountainous terrain, which offered no suitable areas for a safer emergency touchdown.