Lancair LC41-550FG N521RT accident near Carbondale, Illinois

Probable cause

The fatigue fracture and subsequent failure of the No. 2 cylinder exhaust valve during cruise flight, which resulted in a total loss of engine power.

NTSB analysis

The pilot reported that, during cruise flight, the airplane experienced a momentary loss of engine power. While diverting to the nearest airport and completing the emergency checklist items, the engine lost total power, and the pilot chose to make a forced landing to a nearby field. During the landing roll, the airplane's right wing struck a power utility pole before the airplane impacted a ditch and came to rest in a nose-low attitude. A postaccident engine examination revealed that the piston for the No. 2 cylinder had fractured into numerous pieces. Additionally, the exhaust valve head for the No. 2 cylinder had fractured perpendicular to the stem direction where the valve protrudes into the cylinder head during normal operation. The fracture surface of the exhaust valve stem exhibited a series of crack arrest marks consistent with a fatigue crack propagation. Oxidization of the fracture surface was consistent with prolonged exposure to a combustion environment. The fatigue fracture was likely due to extreme temperature gradients experienced along the exhaust valve in the area above the valve seat. A review of available flight data established that the engine had been operated in a manner consistent with the pilot operating handbook. However, without a complete historical flight data record, it was not possible to determine if the engine had been operated outside of its normal operating limits at some point since its original manufacture.

Text from the NTSB. Open the NTSB docket for CEN11FA227 for the full record.