Primary finding
Probable cause
Overheating of the engine coolant for reasons that could not be determined, which resulted in a precautionary off-airport landing, during which the airplane sustained substantial damage.
Investigator assessment
Analysis narrative
The pilot stated that, about five minutes after departure in his experimental amateur-built airplane, the engine coolant began to overheat. The pilot reduced engine power hoping that the coolant temperature would decrease or would not increase further; however, the temperature continued to increase, and the pilot chose to land in a field. During the landing, the airplane contacted a drainage ditch, resulting in substantial damage to the fuselage and the left wing. Postaccident examination of the automotive engine revealed no evidence of coolant leaks, and the coolant overflow tank was full of coolant. The cause of the overheating was not determined during the examination. The pilot stated that he had not experienced any issues with overheating coolant during previous flights.
Source record
Factual narrative
On September 2, 2024, at 0914 central daylight time, an experimental, amateur-built CH601 XL, N624RJ, sustained substantial damage when it was in involved in an accident near Odessa, Missouri. The pilot and a pilot-rated passenger received minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot, who was also owner of the airplane, stated that about five minutes after departure, the engine coolant temperature began to rise rapidly. The pilot then turned the airplane toward the departure airport and reduced engine power and airspeed. The pilot continued to decrease engine power, hoping that the coolant temperature would decrease or would not increase. The pilot then decided to attempt a landing at a closer airport, and the coolant temperature continued to increase. Steam and an odor filled the cockpit, and the pilot decided to land in a field. During the landing, the airplane impacted a shallow drainage ditch, resulting in substantial damage to the fuselage and left wing. Postaccident examination of the airplane by a Federal Aviation Administration inspector revealed that the airplane was powered by an automotive engine. The examination revealed that there were no coolant leaks, and the coolant overflow tank was full of coolant. The cause of the overheat could not be determined. The pilot stated that he had not experienced coolant overheating during previous flights, and he did not know why the overheating occurred during the accident flight.