CEN23FA144 · Zenith STOL CH701

After takeoff, the pilot proceeded south and then southwest. About 16 miles from the airport, the pilot reversed course and proceeded toward the north and then the northeast, in the general direction of the departure airport. The airplane subsequently entered a right turn toward the south; however, the position data ended about 11 seconds later. The airplane subsequently impacted trees and terrain about one-third mile south of the final data point. A review of the available flight track data, as well as the wreckage disposition, did not reveal any evidence of an in-flight loss of control. An on-scene airframe examination did not reveal any evidence of an in-flight structural failure or preimpact flight control anomaly. A postrecovery engine examination did not reveal any anomalies consistent with an inability to produce rated power. However, testing of the ignition modules revealed that they both misfired when operating in a narrow range about 4,000 rpm. While the observed anomaly could have resulted in rough engine operation at that specific engine speed, it likely would not have resulted in a loss of engine power. An autopsy revealed the pilot had severe narrowing of a single coronary artery. His coronary artery disease conveyed increased risk of a sudden impairing or incapacitating cardiac event such as unstable arrhythmia or heart attack. There was no autopsy evidence that such an event occurred, but such an event leaves no reliable autopsy evidence if it occurs immediately before death. The limited available information about the circumstances of the crash adds little clarity about the likelihood of a medical event. Thus, whether the pilot’s coronary artery disease contributed to the accident cannot be determined. Toxicology testing revealed that ethanol was detected at a low level in cavity blood, a specimen type in which n-propanol was also detected. Ethanol was not detected in vitreous fluid, which is generally the specimen type best protected against postmortem ethanol formation. These results indicate that some or all the small amount of detected ethanol may have been from postmortem production, and that ethanol effects did not likely contribute to the accident. In light of the lack of any significant anomalies with respect to the airplane examinations, and an inability to attribute the event to the pilot’s coronary artery disease and an in-flight medical event, the investigation was unable to determine the specific reason for the impact with the trees and terrain.

Verbatim NTSB analysis and probable cause from the NTSB dataset