Incident Overview
During cruise flight at an altitude of 6,000 feet, approximately 15 minutes after takeoff, a multiengine airplane suffered a catastrophic failure of its right engine. The pilot decided to return to the departure airport, which was located 30 miles from the incident site, rather than diverting to a suitable alternate airport situated about 10 miles away.
Accident Sequence
The pilot reported an inability to maintain altitude following the engine failure. Consequently, the aircraft descended and struck trees before impacting the ground approximately three miles from the departure airport. Post-accident examinations revealed that the majority of the wreckage was consumed by fire. A significant structural defect was identified in the top right portion of the crankcase, where a 5.5 by 6-inch hole was observed.
Technical Findings
Investigation of the right engine determined that the No. 2 cylinder had separated from the crankcase during flight. Two studs associated with this cylinder exhibited fatigue fractures consistent with insufficient preload on their respective bolts. Additionally, a fatigue fracture was found on the right side of the crankcase, oriented mostly perpendicular to the threaded bore of the cylinder stud.
Measurements indicated that the rear top 3/8-inch and 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 inches and .111 inches, respectively. The aircraft had accumulated approximately 50 hours of flight time since its last annual inspection, which occurred eight months prior to the accident. The right engine had operated for about 1,425 hours since overhaul and approximately 455 hours since the No. 2 cylinder was removed for the replacement of six cylinder studs.
Contributing Factors
While it remained unclear why the pilot was unable to maintain altitude after the power loss, investigators noted that the aircraft was capable of reaching an alternate airport had the pilot chosen not to return to the departure point.