Aircraft Accident During Approach Briefing at FL 330 (SE-DUX)

Event Sequence and Instrument Malfunction The flight was uneventful until 00:19:20 hrs during darkness without moonlight, clouds, or turbulence. The event began during an approach briefing in level flight at FL 330. With no external visual references, the pilots relied entirely on instruments, including three independent attitude indicators. Recorded data and simulations showed a very fast increase in pitch displayed on the left attitude indicator. The pilot in command, who was the pilot flying in the left seat, exclaimed a strong expression. This displayed pitch change caused a surprise effect and degradation of spatial orientation. The autopilot was most probably disconnected automatically, a “cavalry charge” aural warning sounded, and a single chime was heard, likely due to a miscompare between the left and right pilots’ flying displays (PFDs). Both elevators moved toward nose down, and nose-down stabilizer trim was gradually activated from the left control wheel trim switch. The aircraft began to descend, with angle of attack and G-loads becoming negative. Both pilots exclaimed strong expressions, and the co-pilot said “come up.” ## Crew Response and Spatial Disorientation About 13 seconds after the event started, the crew faced two contradictory attitude indicators with red chevrons pointing in opposite directions. No comparator caution was displayed due to the PFDs’ declutter function in unusual attitude. Bank angle warnings were heard, and 17 seconds after the start, the maximum operating speed and Mach number were exceeded, activating the overspeed warning. Speed continued to increase, a distress call was transmitted and acknowledged by air traffic control, and engine thrust was reduced to flight idle. The crew remained active throughout, with dialogue mainly concerning different perceptions of turn directions and the need to climb. At this stage, the pilots were probably subjected to spatial disorientation. The aircraft struck the ground one minute and twenty seconds after the initial height loss. Both pilots were fatally injured, and the airplane was destroyed.