Amateur-built 601XL accident near Albertville, Alabama, June 3, 2023

The NTSB's narrative final · quoted from the NTSB record

After troubleshooting oil pressure and airspeed indications issues with his electronic flight instrumentation and engine monitoring system, the pilot departed in the experimental amateur-built airplane on its third test flight. Data recovered from the airplane’s onboard electronic instruments showed that the airplane departed the airport traffic pattern and flew for about 30 minutes, performing several heading changes and climbing to 4,000 ft mean sea level (msl) before descending to level off at 2,050 ft msl. There was nothing unusual about the airplane’s flight profile and the maneuvers up to that point appeared to be normal. Witnesses to the final moments of the flight reported the airplane was flying slow at a low power setting. One witness reported the airplane stalled or pitched up and down, then stalled again before it rolled to the left and right and then descended behind the trees. Another witness reported the engine power increased to full power before the nose of the airplane pitched down. The pilot did not recover from the descent and the airplane impacted trees and terrain about 3 miles away from the airport. The recorded data for the final moments of the flight revealed a sequence of events that was generally consistent with the witness observations, and there were no apparent anomalies with the airplane’s engine preceding or during the final descent. Postaccident examination of the airframe, systems, and engine did not reveal evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation. Discrepancies observed in the recorded data, such as recorded changes to the roll angle and a relative lack of change of the airplane’s heading and ground track, as well as differences between the airplane’s indicated/true airspeeds and the recorded GPS groundspeeds suggested that the troubleshooting efforts the pilot was performing to the airplane’s electronic instruments may not have resulted in the system being fully functional and able to record reliable parametric data. Medical examination revealed the pilot was at increased risk of cardiovascular disease. No significant cardiovascular disease was identified during the pilot’s autopsy; however, the autopsy was limited by injuries that prevented examination of the pilot’s coronary arteries. Toxicology testing of specimens from the pilot was consistent with medication-treated diabetes, without severe high blood sugar at the time of the accident. While this condition was associated with some increased risk of impairment or incapacitation, there was no specific forensic evidence that a medical event contributed to the accident. Based on the available evidence, the reason for the airplane’s descent and impact with terrain could not be determined.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.