John M. White

The multiengine airplane was at an altitude of 6,000 feet when it experienced a catastrophic right engine failure, approximately 15 minutes after takeoff. The pilot elected to return to his departure airport, which was 30 miles away, instead of diverting to a suitable airport that was located about 10 miles away. The pilot reported that he was not able to maintain altitude and the airplane descended until it struck trees and impacted the ground, approximately 3 miles from the departure airport. The majority of the wreckage was consumed by fire. A 5 1/2 by 6-inch hole was observed in the top right portion of the crankcase. Examination of the right engine revealed that the No. 2 cylinder separated from the crankcase in flight. Two No. 2 cylinder studs were found to have fatigue fractures consistent with insufficient preload on their respective bolts. In addition, a fatigue fracture was observed on a portion of the right side of the crankcase, mostly perpendicular to the threaded bore of the cylinder stud. The rear top 3/8-inch and the front top 1/2-inch cylinder hold-down studs for the No. 2 cylinder exceeded the manufacturer's specified length from the case deck by .085 and .111 inches, respectively. The airplane had been operated for about 50 hours since its most recent annual inspection, which was performed about 8 months prior the accident. The right engine had been operated for about 1,425 hours since it was overhauled, and about 455 hours since the No. 2 cylinder was removed for the replacement of six cylinder studs. It was not clear why the pilot was unable to maintain altitude after the right engine failure; however, the airplane was easily capable of reaching an alternate airport had the pilot elected not to return to his departure airport.

The pilot was maneuvering the airplane south of the airport preparing to make a VFR approach. Witnesses observed the airplane in a right spin. NTAP data showed the airplane to be well above stall speed before disappearing from radar. Examination of the radar data revealed that in 6 seconds, ground speed dropped 31 knots, from 200 knots to 169 knots, and altitude dropped 440 feet, from 11,760 feet to 11,320 feet (4,400 feet per minute). In the next 6 seconds, ground speed dropped another 31 knots, from 169 knots to 138 knots, and altitude dropped 1,020 feet, from 11,320 feet to 10,300 feet (10,200 feet per minute). According to the manufacturer, if the throttles were to be brought back into Beta (flat pitch) range, it is possible that one propeller could go into Beta an instant before the other propeller. If this were to happen, the airplane would instantly snap roll and enter a spiral. The pilot had received an estimated 4 hours of dual instruction in the airplane.