CEN23FA332

The pilot and passenger departed on a local flight and climbed to an altitude of about 3,900 ft mean sea level (msl) while turning to overfly a local lake. After leveling off, the airplane made a turn to the right, followed by a turn to the left. Performance calculations based on ADS-B and winds aloft data showed that, during the turns, the airplane decelerated, and the calculated load factor increased. The airplane slowed to a speed consistent with its published accelerated stall speed, then entered a rapid descent. A witness reported seeing the airplane in a flat spin to the right that continued until the airplane impacted the water. The airplane was destroyed when it impacted the water. Examination of the airplane, engine, and related systems did not reveal any preimpact anomalies that would have precluded normal operation. Based on the available information, the pilot likely failed to maintain adequate airspeed while maneuvering and exceeded the airplane’s critical angle of attack, which resulted in an inadvertent aerodynamic stall/spin.

On July 29, 2023, at 0905 central daylight time, a North American AT-6D airplane, N49961, was destroyed when it was involved in an accident near Oshkosh, Wisconsin. The pilot and the passenger were fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The airplane was at the annual Experimental Aircraft Association AirVenture fly-in, held at Wittman Regional Airport (OSH), Oshkosh, Wisconsin. According to ADS-B flight track data, the airplane departed from runway 27 at OSH about 0857. The airplane made a right turn toward the north and continued about 3 miles before it turned toward the east-northeast. The flight path took the airplane over Lake Winnebago, outside of the OSH Class D airspace. The airplane proceeded out over the lake and reached a peak altitude of 3,900 ft, before it descended rapidly into the lake at 0905. (See figures 1 and 2). Performance calculations based on ADS-B and winds aloft data revealed that, during the final portion of the flight, the airplane leveled off at 3,900 ft msl and made a right turn followed by a left turn before the rapid descent. After leveling off, the airplane’s calibrated airspeed (CAS) was about 110 mph. During the subsequent turns, the airplane slowed, reaching its lowest speed of 87 mph CAS just before the rapid descent. The airplane’s calculated load factor during the second turn reached about 1.8 g. The published 1g stall speed (wings level) for the airplane with landing gear and flaps retracted was 67 mph at a loaded weight of 5,500 lbs. Based on the calculated load factor, the airplane’s accelerated stall speed at that weight would have been about 89 mph. A witness who was in a boat on the lake reported seeing the airplane about 1 to 1.5 miles from his position and about 30° above the horizon. He described the airplane as being in a flat spin to the right and he did not hear any noise. The airplane continued to spin until it impacted the water. The airplane broke into pieces and came to rest at the bottom of the lake in about 20 ft of water. Figure 1. ADS-B flight track with the accident location depicted by a white circle. Figure 2. The final portion of the airplane’s flight path. The Walworth County Medical Examiner, Elkhorn, Wisconsin, performed the pilot’s autopsy. According to the autopsy report, the pilot’s cause of death was multiple blunt force injuries. Toxicology testing performed by the FAA Forensic Sciences Laboratory on the pilot’s specimens did not identify any substances that are generally considered impairing. According to the pilot’s flight logbook, at the time of the accident she had accumulated 687.8 total hours of flight experience, including 33 hours in the accident airplane make and model. An entry dated May 26, 2023, for a 1.0-hour flight, was noted as being a checkout flight for the AT-6D airplane, but the entry did not specify maneuvers performed. A postaccident examination of the airplane was conducted after itsrecovery from the lake. The fuselage was broken into two main pieces, with the break at the aft end of the rear-seat cockpit where the aluminum aft fuselage structure was bolted to the forward steel tube fuselage structure. The cockpit consisted of a steel tube cage from the firewall to the rear end of the aft cockpit. The tube cage was covered in an aluminum skin. The tube structure was mainly intact, but there was significant crush-damage in the front cockpit area. The horizontal stabilizer and vertical stabilizer surfaces remained attached to the aft fuselage and were mostly undamaged. The elevators remained attached to the horizontal stabilizer and both the elevator trim tabs were still attached to the elevators. The left inboard elevator surface was impact damaged. The right elevator displayed impact damage at both the inboard and outboard ends. The elevator trim tabs were both deflected downward relative to the elevator surface (up elevator trim) but the deflection was not consistent between the right and left tabs, with the right deflected about 30 degrees and the left deflected about 23 degrees. The torque shaft that connected the right and left elevator halves was twisted and broken adjacent to the right elevator. The rudder was separated from the vertical stabilizer, but remained partially attached to the airplane via the rudder control cables. The rudder trim tab was still attached and was in a neutral position. The right wing was separated from the airplane adjacent to the right side of the fuselage. The section of wing outboard of the wing joint between the center section and outboard panel was intact, but with significant impact damage. The leading edge was crushed upward and rearward just outboard of the wing joint. The split flap remained attached to the wing and the aileron was separated. The left wing remained attached to the fuselage and was bent downward just outboard of the wing joint. The leading edge was crushed rearward and upward. The split flap remained attached to the wing and the aileron was separated. The wing center section remained attached to the fuselage steel tube cage. The right portion of the center section was separated consistent with impact damage, even with the fuselage's right side. The left side of the center section was heavily damaged at the leading edge. The left landing gear was still attached to the wing center section and was in the extended position during examination. The right landing gear was still attached to a portion of the wing center section spar but had separated from the remainder of the wing. The landing gear was in the extended position as examined. Examination of the primary flight control system (aileron, elevator, rudder) revealed breaks to all of the primary flight controls, but all of the breaks exhibited features consistent with impact damage. The propeller was still attached to the engine. One blade was bent rearward, and one blade was relatively straight. The bent bladeprevented engine rotation, and the bent portion was cut off. The engine was subsequently rotated by hand after the removal of one set of spark plugs. Compression and suction could not be verified on all cylinders due to bending of the forward-mounted pushrods. The rocker covers on several cylinders were removed to verify valve action and valve train continuity. No airframe, control system, or engine anomalies were found that would have precluded normal operation.