Incident Summary
The commercial pilot, who held 1,800 hours of flight experience, reported that while the airplane was in cruise flight, the left engine ceased producing power and the left propeller moved forward approximately six inches. The pilot secured the engine and executed a precautionary forced landing to a field. The airplane sustained substantial damage during the landing.
Aircraft History
A review of the aircraft maintenance records disclosed that the airplane had experienced a gear-up landing in January 2002, which resulted in a propeller strike. Following that incident, the left engine was removed and inspected in accordance with the manufacturer's overhaul manual before being returned to service. At the time of the current event, the engine had accumulated approximately 440 hours since that overhaul.
Engine Examination
Post-incident examination of the engine revealed that the entire three-bladed propeller assembly and the No. 1 cylinder had separated from the engine. The engine was disassembled, and the crankshaft, along with an intact No. 3 connecting rod assembly and the fractured No. 2 connecting rod assembly, were examined by a Safety Board Materials Engineer.
Crankshaft Analysis
The crankshaft exhibited fractures in two locations: one fracture was located just forward of the No. 3 rod journal in the crank cheek, and the other fracture was in the aft crank cheek adjacent to the No. 2 main journal. The interior surfaces of the No. 1 and No. 2 main bearing halves showed significant rubbing, and a portion of the bearing liner material was delaminated and missing from the forward end of the bearing. On the oil slinger face, just forward of the No. 1 main journal, 360-degree rubbing damage was noted just outboard of the radius. In the rub region, metallic transfer consistent with aluminum material was observed. No evidence of radial cracks was found in this area.
An exact determination for the crankshaft failure could not be identified; however, evidence supported two possible scenarios. One possibility was that the crankshaft fracture initiated from rubbing damage between the crank cheek aft of the No. 2 main journal (thrust face) and the crankcase, with the other fatigue region being secondary. The specific cause of the rubbing was unclear, but one potential explanation was that the bearing liner delaminated and released a section, reducing the clearance between the crankshaft and crankcase as it rubbed against or exited through the oil slinger. The other possibility was that the propeller strike induced the rubbing or cracking, which was not detected during the subsequent overhaul and inspection.