DRAGONFLY-C N667DF accident near Darbyville, Ohio

Probable cause

The total loss of engine power due to a cold-seizure event that occurred at a low altitude, which precluded the pilot's recovery from an inadvertent aerodynamic stall/spin.

NTSB analysis

The accident occurred during an aero-tow of a hang glider. The pilot reported that during initial climb, about 80 feet above the runway, the airplane experienced a sudden and total loss of engine power while it was in a climbing left turn. He stated that the airplane immediately entered an aerodynamic stall/spin following the loss of engine power. The pilot released the towed hang glider, but he was unable recover from the aerodynamic stall condition before the airplane impacted terrain. A postaccident examination of the two-cylinder engine revealed excessive piston scoring within one of the cylinder assemblies and excessive wear on the piston wrist-pin. The observed anomalies were consistent with a cold-seizure event. A cold-seizure event is a thermo-imbalance condition between the piston and cylinder, which results in an insufficient clearance between the piston and the cylinder. The cylinder thermo-imbalance condition is typically the result of an insufficient engine warm-up period before takeoff power is applied. However, the conditions that led to the cold-seizure event may not have been limited to the accident flight. The total loss of engine power during initial climb, while towing a hang glider, likely contributed to the aerodynamic stall/spin encountered at a low altitude. Additionally, the low altitude at which the aerodynamic stall/spin was encountered was likely insufficient to have allowed a recovery before the airplane impacted terrain.

Text from the NTSB. Open the NTSB docket for CEN13LA055 for the full record.