N234MTRaytheon Aircraft B36TC · 2000

On March 2, 2008, about 1620 Pacific standard time, a Beechcraft B36TC, N234MT, collided with snow that was covering level terrain about three miles south of Mammoth Yosemite Airport, Mammoth Lakes, California. The private pilot received minor injuries, his passenger received serious injuries, and the airplane, which was owned and operated by the pilot, sustained substantial damage. The 14 Code of Federal Regulations (CFR) Part 91 personal cross-country flight, which departed Mammoth Yosemite Airport about five minutes prior to the accident, had a planned destination of Van Nuys, California. The pilot had not filed a flight plan.

According to the pilot, three or four minutes after takeoff, the engine experienced a "major loss in power." He therefore turned back toward the airport and began to take action to try to restore full power. During this process he switched fuel tanks, checked the magnetos, activated the fuel boost pump to the prime position, and switched to alternate induction air. Ultimately, although the propeller kept turning, the engine lost all power, and the pilot began to look for what he thought would be a safe place to land. He elected to execute a forced landing on level snow-covered terrain in what appeared to be an open field. He then configured the airplane for a normal landing, and touched down in about three feet of dense snow with the landing gear extended. Upon touchdown, the landing gear broke through the surface of the snow, and as the airplane sank into the snow it decelerate rapidly. The accident sequence resulted in crushing damage to the airplane's belly and to the inboard portion of both wings.

During the investigation it was determined that at the time of takeoff, the airplane contained about 65 gallons of aviation fuel, which was evenly distributed between the right and left fuel systems. The wreckage was recovered to the facilities of Air Transport, of Phoenix, Arizona, where an FAA-directed inspection of the airframe and engine was performed. That inspection did not reveal any anomalies in the airframe, its air induction system, or its fuel delivery system. After a visual inspection, the engine was successfully run at various power settings up to 2,400 rpm and 30 inches of manifold pressure.

As part of the investigation the turbocharger turbine/compressor assembly, pressure relief valve, variable absolute pressure controller, and exhaust bypass valve assembly were sent to Kelly Aerospace Power Systems, where an FAA-monitored teardown inspection was performed. That inspection did not reveal any evidence of anomalies or malfunctions that would have prevented these components from operating in accordance with field serviceable standards.