Beechcraft A36 N19MT

About 18 minutes after takeoff, while on an instrument flight rules (IFR) flight, the pilot requested a lower altitude, advising the controller that the airplane’s climb performance was degraded. As the flight continued the pilot recognized a “dead cylinder” and requested a heading to a nearby airport. The controller vectored the flight to the airport, but the pilot delayed turning onto the vectored heading for over 2 minutes. When the flight was about 6 nautical miles from the airport the pilot declared an emergency and advised the controller that the oil pressure was dropping. After turning onto the vectored heading, the airplane began a right turn that was not directed by the controller or announced by the pilot. The controller informed the pilot to level the wings and maintain 5,000 ft msl. The change in the airplane’s heading resulted in the controller providing a new vector, which increased the distance and flight time to the intended runway. Recorded data showed the engine then lost all power. The airplane continued to descend and subsequently collided with trees and the ground less than 1 mile from the intended runway threshold. According to recorded data, shortly after takeoff, when the flight was about 1 nautical mile from the departure end of the runway, the No. 4 cylinder head temperature (CHT) value exceeded the highest allowed value. The flight continued while the No. 4 CHT continued to increase. The CHT for that cylinder then began to decrease, consistent with non-firing of the fuel air mixture, and the flight continued. Postaccident examination of the engine revealed damage to the top and sides of the No. 4 piston that were likely the result of pre-ignition/detonation that pressurized the crankcase, pushing oil out of the breather assembly and depleting the oil supply. This ultimately resulted in oil exhaustion and subsequent catastrophic internal engine failure. Both spark plugs of the No. 4 cylinder had extensive deposits and one had a separated section of core nose insulator while the other only had a cracked core nose insulator, though it could not be determined from the available evidence if those conditions existed before or were the result of pre-ignition/detonation. Causes for detonation include improper ignition timing, high inlet air temperature, engine overheating, carbon build-up or oil in the combustion chamber, an issue with the fuel octane, or a lean fuel-to-air mixture. Although the magneto-to-engine timing could not be determined postaccident, there were no postaccident anomalies noted with either the magneto or the ignition harness. High inlet air temperature, engine overheating, or carbon build-up/oil in the combustion chamber were not likely or not observed. There was no report of any fuel-related issue from the facility that last fueled the accident airplane. While the position of the mixture control during the flight and the pilot’s leaning procedures were unknown, it is unlikely that the pilot would have leaned the fuel-to-air ratio to CHT exceedance as that would have been contrary to the published limitations and takeoff procedures.

Quoted verbatim from the NTSB record.