The pilot, who held a commercial rating, and passenger, who held an airline transport pilot (ATP) rating, departed in the morning on a multi-leg personal flight. They accumulated about 8.5 hours of flight time that day, having stopped at 2 en route airports for fuel. Their final landing, which occurred in the evening after dark, was at an airport located about 21 miles from their destination. The pilots communicated to the airplane owner that they had stopped for additional fuel in the event of a missed approach at their final destination.  Before takeoff, they received an instrument flight rules (IFR) clearance, which consisted of an assigned heading of 090 and a climb to 3,000 ft above mean sea level (msl). The airplane departed and no further communications from the pilots was recorded by air traffic control.ADS-B data indicated that after departure, the airplane climbed to 1,775 ft msl and began a right turn, which was opposite the direction of their destination. After turning about 90°, the airplane made a rapid descending right turn, and the recorded data showed the airplane at 1,275 ft msl (505 ft above ground level [agl]). The airplane continued to descend until it impacted a vacant construction site in a right-wing-low orientation. The airplane came to rest about 80 ft from the initial impact point. A postimpact fire consumed most of the wreckage. Nearby surveillance video captured audio of the airplane’s departure and both audio and video of the accident sequence. During the video, no abnormal engine sounds were heard. A witness located near the accident location stated that the airplane appeared to be at a “low altitude, right-hand bank at a high rate of speed” just before the impact. He stated that the engine sounded as if it was operating at a high power setting. The airplane impacted a vacant construction site and a postimpact fire consumed a majority of the wreckage. Page 2 of 12 CEN23FA057At the time of the accident, the departure airport was reporting instrument meteorological conditions (IMC) with an overcast ceiling at 300 ft and visibility of 2.5 statute miles. Astronomical twilight had ended at 1851, about two hours before the accident, with night instrument conditions prevailing at the time of departure Conditions were cloudy from about 1,300 ft through 4,200 ft agl. Although the postaccident examination of the airframe and engine was limited due to the significant impact and fire damage, the examination revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. The airplane’s flight instruments and avionics were destroyed during the accident and were unable to be functionally tested. The investigation was unable to determine which pilot was manipulating the flight controls at the time of the accident.An aircraft performance study showed that the airplane tracked the extended centerline of the runway then began a right turn. About 20 seconds later, the airplane was descending rapidly, the airspeed was increasing through 140 kts, the pitch angle was decreasing past -10°, and the roll angle was increasing past 60°. The descent rate exceeded 11,000 ft/min. The total calculated energy showed a steady increase over the course of the flight consistent with the engine operating at a high power setting.The rapid descent after the initial right turn was consistent with the pilot experiencing spatial disorientation in night instrument conditions, which resulted in a loss of control and high-speed impact with terrain. Given the long day of flying, and the night instrument conditions encountered during departure, it is likely that the pilot experienced spatial disorientation and lost control of the airplane.