What happened
While cruising at FL 330 in level flight, the crew began an approach briefing during nighttime conditions. The environment was characterized by a lack of moonlight, clouds, or turbulence, leaving the crew entirely dependent on flight instruments. During this period, a sudden and rapid increase in pitch was recorded on the left attitude indicator. This unexpected change caused a significant loss of spatial orientation for the pilot in command.
Following this event, the autopilot likely disconnected, accompanied by a cavalry charge aural warning and a single chime, likely triggered by a miscompare between the primary flight displays. The aircraft's elevators moved toward a nose-down position, and the nose-down stabilizer trim was activated via the left control wheel trim switch. As the aircraft descended, it experienced negative G-loads and an increasing angle of attack.
Approximately 13 seconds into the event, the crew faced contradictory attitude indicators showing opposing red chevrons. Due to the aircraft's unusual attitude, the declutter function on the flight displays prevented comparator cautions from being shown. As the descent continued, the aircraft exceeded its maximum operating speed and Mach number 17 seconds after the initial disturbance, triggering an overspeed warning.
In an attempt to manage the situation, the crew reduced engine thrust to flight idle and transmitted a distress call, which was acknowledged by air traffic control. The crew remained active throughout the sequence, though their communication was primarily focused on conflicting perceptions of turn directions and the need to climb. The aircraft struck the ground one minute and twenty seconds after the initial loss of altitude. The accident resulted in two fatalities and the total destruction of the aircraft.
Findings
- The crew suffered from spatial disorientation due to a lack of external visual references and sudden instrument discrepancies.
- A significant pitch change on the left attitude indicator created a surprise effect for the pilot in command.
- The aircraft's flight displays entered a declutter mode during the unusual attitude, which suppressed critical comparator cautions.