Incident Summary
On September 18, 2011, about 1035 eastern daylight time, a Beech V35, registration N275BM, operated by a commercial pilot, sustained minor damage during a forced landing following a total loss of engine power shortly after takeoff from Tweed-New Haven Airport (HVN), New Haven, Connecticut. The pilot and a passenger were not injured. Visual meteorological conditions prevailed and an instrument flight rules flight plan was filed for the personal flight conducted under 14 CFR Part 91.
According to the pilot, the airplane departed HVN and climbed without incident. As it approached 6,000 feet mean sea level, the pilot felt a shudder and a slight change in engine rpm. Seconds later, oil appeared on the windscreen, accompanied by smoke and engine roughness, followed by a total loss of engine power. The pilot declared an emergency and returned to HVN for a forced landing on runway 14. During landing, the airplane overran the runway by about 50 feet, causing minor nose gear damage, and came to rest in weeds.
Aircraft Information
The Beech V35 was powered by a Teledyne Continental Motors IO-550-B83, 300-horsepower engine, equipped with a three-bladed Hartzell constant-speed propeller. At the time of the incident, the airplane had accumulated approximately 5,470 total hours and 14 hours since its most recent annual inspection on August 11, 2011. The engine was manufactured in November 2006 and had operated for about 910 total hours, including about 500 hours since maintenance that involved reinstallation of the Nos. 2 and 4 cylinders after repair on February 17, 2009.
Examination and Findings
A Federal Aviation Administration inspector examined the airplane and discovered that the propeller and forward portion of the crankshaft, aft of the propeller mounting flange, had separated in flight and were subsequently located in a wooded area. The engine and separated crankshaft portion were retained for further examination.
A teardown of the engine at Continental Motors Inc., Mobile, Alabama, supervised by an NTSB investigator, revealed that the crankshaft and counterweight assembly exhibited lubrication distress, thermal damage, and mechanical damage on all six connecting rod journals. The crankshaft was fractured into two pieces across the No. 4 main journal. The crankcase main bearing supports adjacent to the fracture showed fretting signatures and lock-slot elongation. The No. 4 main bearing was extruded, with portions found in the oil sump. Metallurgical examination of the fractured crankshaft indicated that cracks initiated on the bearing surface near an oil transfer tube and propagated in fatigue; additional cracks were identified on the bearing fillet radius.