CEN23LA419

According to the pilots, the airplane operated normally during the first two hours of the cross-country instructional flight. The flight instructor reported he then noticed the fuel flow seemed a little high. When the flight instructor reduced the mixture setting, the engine began to run rough. The instructor increased the mixture, which smoothed the engine roughness. The engine ran rough again, and the instructor once again increased the mixture setting, which smoothed the engine roughness. The engine then ran rough two additional times; both times the instructor increased the mixture setting, causing the roughness to cease. The engine roughness occurred again but was worse than he previously experienced. The instructor increased the mixture control to its full forward position and decided to divert to an alternate airport. The engine lost power while en route to the alternate airport, and the flight instructor performed a hard gear-up forced landing in a field, resulting in substantial damage to the fuselage and wings. Postaccident examination of the airplane revealed an adequate amount of fuel was present and a postaccident engine test run revealed no mechanical anomalies that would have precluded normal engine operation.

On September 23, 2023, at 1625 central daylight time, a Beech A36, N67CD, was involved in an accident near El Dorado, Arkansas. The airplane sustained substantial damage. The pilot and a flight instructor received minor injuries. The airplane was operated under Title 14 Code of Federal Regulations Part 91 as an instructional flight. The airplane engine was equipped with a turbocharger through a supplemental type certificate installation. About six weeks before the accident flight, the airplane exhibited a loss of engine power. The accident flight was a cross-country flight to provide the pilot/airplane owner with training required by the pilot’s insurance carrier. During the accident flight, the airplane operated normally during the first two hours of the flight but was then followed by a fuel flow/consumption rate of about 22 gph, which seemed a little high to the flight instructor. When the instructor tried to reduce the mixture setting, the engine began to run rough, which he thought was unusual. They advanced the mixture, and the engine smoothed out. The engine then began to run rough again, and the instructor increased the mixture setting, which smoothed the engine roughness. The engine began to run rough again, and the instructor increased the mixture setting again, which smoothed the engine roughness. The engine then ran rough two additional times; both times the instructor increased the mixture setting, causing the engine roughness to cease. The engine roughness occurred again but was worse than the roughness they previously experienced. The instructor increased the mixture control to its full forward position and decided to divert to an alternate airport. The engine lost power while en route to the alternate airport, and the flight instructor performed a forced landing to a field. During the landing, the airplane sustained substantial damage to the fuselage and wings. During the recovery of the airplane from the accident site, about 50 gallons of 100 low lead aviation fuel was drained from the aircraft. The left wing fuel tank contained about 20 gallons of fuel and the fuel within the right wing fuel tank had drained onto the ground due to an impact-related breach of the right wing fuel tank. The auxiliary fuel tanks had an unknown quantity of fuel. During a postaccident test run of the engine, power settings from idle to maximum power were used. The engine started without hesitation and ran smoothly and without the symptoms that occurred during the accident flight. No anomalies that would have precluded normal operation were present during the test run. Maintenance records indicate the engine was sent out for overhaul and was reinstalled on the airplane about one month before the accident. A maintenance entry dated 12 days before the accident indicated the fuel pump was adjusted to set the fuel flow to 35.9 gallons per hour at full power.