Amateur-built GT-500 N599RA accident near Willows, California

Probable cause

A loss of engine power during takeoff due a coolant leak and the subsequent overheating of the engine, and the student pilot's failure to maintain airspeed and his exceedance of the airplane's critical angle of attack, which resulted in an aerodynamic stall and collision with terrain. Contributing to the accident was inadequate maintenance inspection and the flight instructors delayed remedial action.

NTSB analysis

The flight instructor and the student pilot, who was the pilot flying, departed for the third leg of the cross-country flight. The student pilot indicated that shortly after takeoff, when the airplane was about 70 ft above the runway, the engine sputtered and then lost power. He stated that he attempted to land straight ahead but did not maintain proper airspeed. The video from an onboard camera showed that after the engine lost power, the student pilot pulled back on the yoke, and the airplane rapidly descended toward the runway and impacted the ground likely following an aerodynamic stall.

Postaccident examination of the engine revealed that the radiator coolant level was low enough that the fluid was not visible through the radiator cap. The examination revealed a coolant leak around the water pump housing nipple due to an improper seal of the hose to the nipple attachment. In addition, the radiator recovery and overflow bottle were improperly installed, which prevented the system from refilling coolant into the radiator during the engine cooling period in between flights. The intake port sides of the cylinders had antifreeze particles embedded into their surfaces consistent with overheating. The top portion of the No. 1 piston exhibited melted metal deposits from spark plug electrodes consistent with preignition and detonation, and the No. 2 piston exhibited discoloration and burnt-on carbon deposits consistent with the piston overheating for a period of time.

It is likely that the airplane had lost a significant amount of coolant during the previous legs of the cross-country flight, which led to an overheated cylinder and subsequent engine failure. In addition, the student pilot failed to maintain airspeed after the partial loss of engine power. The airplane exceeded its critical angle of attack, which resulted in an aerodynamic stall at an altitude too low to recover.

Text from the NTSB. Open the NTSB docket for WPR18LA036 for the full record.