Amateur-built Sonex HB N244HB accident near Plainview, Illinois

Probable cause

The loss of engine power during cruise flight due to a fatigue fracture of the crankshaft, which resulted in a forced landing on unsuitable terrain.

NTSB analysis

The private pilot and a sport pilot-rated passenger were conducting a personal cross-country flight in the experimental amateur-built airplane, which was powered by an uncertified automotive engine. The airplane was in cruise flight when it experienced a total loss of engine power. The pilot(s) attempted a forced landing on a field, during which the airplane nosed over. The wreckage path through the field was about 200 ft long, which was consistent with excessive energy/speed upon touchdown.

A review of maintenance logbook entries revealed that the engine had been assembled by the owner and that the camshaft and crankshaft had been removed when work was performed on the engine about 3 years before the accident. Postaccident examination of the engine indicated that the crankshaft had fractured due to a fatigue crack that had initiated at a fillet radius at the forward end of the No. 2 main bearing journal where the journal transitioned to the forward cheek. The cause of the fatigue crack could not be determined.

Text from the NTSB. Open the NTSB docket for CEN15LA028 for the full record.