Accident Overview
A twin-engine airplane, operated by a commercial pilot for a business flight, departed from runway 31. During the takeoff roll, the right engine lost power. A pilot-rated witness observed the airplane approximately halfway down the 6,500-foot runway at an altitude of about 100 feet above ground level. The witness heard a loud pop and saw the right propeller slow. The airplane yawed to the right and initiated a right turn toward runway 18, with the right engine's propeller windmilling. The witness noted that the airplane cleared a tree line by about 150 feet, then rolled right, descended straight down, and burst into flames upon impact.
Postaccident Examination
Examination of the right engine revealed a fractured crankshaft adjacent to the No. 2 main bearing, which had rotated. The crankcase halves near the No. 2 main bearing showed fretting around the through-studs. The fretting pattern was consistent with insufficient clamping force due to inadequate torque on the through-stud nuts.
Maintenance History
Records indicated that all six cylinders on the right engine had been replaced during the airplane's most recent annual inspection, eight months before the accident. Replacing the cylinders required removal of the through-stud nuts, as these nuts also secure the cylinders. It is likely that during cylinder replacement, the through-stud nuts were not properly torqued. Over time, this allowed the crankcase halves to move, leading to bearing rotation and crankshaft fracture.
Pilot Actions
During the accident sequence, the pilot executed a right turn in an attempt to return to the airport. He did not feather the failed right engine's propeller, allowing it to windmill and create excessive drag. The pilot likely allowed the airspeed to decay below the minimum required for the airplane to remain controllable. This loss of airspeed, combined with the failure to feather the propeller and the turn in the direction of the failed engine, resulted in a loss of airplane control.
Probable Cause
The official probable cause stated: "The loss of right engine power on takeoff due to maintenance personnel's failure to properly tighten the crankcase through-studs during cylinder replacement, which resulted in crankshaft fracture. Also causal were the pilot's failure to feather the propeller on the right engine and his failure to maintain control of the twin-engine airplane while maneuvering to return to the airport."