Martinaire

During the night before the accident, freezing rain followed later by snow, fell on the ramp where the airplane was parked. A witness reported that while assisting the pilot in removing snow from the airplane, he noted that 80% of the wing was covered with a coarse layer of ice, from 1/16 to 3/16 in thickness, that was not removed before flight. After the accident, a fireman from the city of lubbock fire department noted ice on the wing approximately 1/16th of an inch thick that had a rough texture that looked as if deposited by freezing rain. The pilot reported that shortly after take off she heard a power decrease and felt surges in the aircraft. The pilot then looked for a place to land. A detailed examination of the engine revealed no mechanical deficiencies.

After leveling at 5,500 feet, the standby power annunciator light illuminated, followed by loss of oil pressure. The pilot turned back toward the airport, but there was a progressive loss of engine power and the prop went to a feathered position. During an emergency landing at night, the aircraft hit a power line and trees, then crashed. During an engine teardown, disassembly of the reduction gearbox scavenge pump revealed that a retaining nut and tang washer (w/i the scavenge pump) had backed off and lodged between the spur gears, which resulted in a sheared scavenge pump drive shaft. In turn, this resulted in the loss of oil pressure and allowed the prop to feather.

About 6 minutes after takeoff, at 2138:31 cdt, the pilot reported level at 9,000 feet msl. At 2140:17, he transmitted that he had trouble and said he could not control or disconnect the autopilot (a/p) which was causing the aircraft to descend. At 2141:14, he stated he was descending at 6,000 feet/min. Another company pilot in another aircraft asked if he could find the breaker, meaning the a/p circuit breaker. At 2141:27, the pilot of N8CC replied, 'call you back.' Seconds later, radio and radar contact with N8CC were lost. A search was initiated, but the aircraft was not found until the following morning. An exam revealed the aircraft impacted in a steep, nose down, inverted attitude while at high speed; much of the wreckage was buried. No preimpact part failure/malfunction was found. With the a/p engaged, back pressure on the control column would have caused the a/p to trim nose down. Subsequently, the manufacturer issued a precautionary advisory to all MU-2 owner/operators regarding proper operation of the a/p and the various ways in which it can be disengaged. The pilot, sole on board, was killed.