What happened
On March 11, 2024, a Boeing 787-9 operating a scheduled international passenger flight from Sydney, Australia, to Auckland, New Zealand, experienced a sudden, uncommanded descent while cruising at FL410. During the flight, the captain's seat moved forward without control, causing the pilot's legs to be compressed against the control column. This physical pressure on the column exceeded the autopilot's operational limits, resulting in the inadvertent disconnection of the autopilot's attitude (ATT) mode. The flight crew managed to stabilize the aircraft, reconnected the autopilot, and continued the flight to Auckland. While the aircraft landed safely, the event resulted in three serious injuries, including one flight attendant and two passengers.
The investigation
DGAC Chile conducted an investigation into the incident, which occurred in international airspace. Investigators examined the flight data, maintenance logs, and the physical condition of the cockpit. The inquiry focused on the mechanical failure of the captain's seat, specifically the rocker switch assembly. It was discovered that a flight attendant had inadvertently bumped the switch cover while entering the cockpit, which triggered the seat movement. The investigation also reviewed the maintenance history of the aircraft and the crew's response to the sudden loss of automation.
Findings
- The primary cause of the sudden descent was the uncontrolled forward movement of the captain's seat, which forced the pilot's legs against the control column, triggering the autopilot disconnection.
- The rocker switch assembly on the captain's seat was defective; the switch cap had detached from its structure, leaving the mechanism in an abnormal, unstable position.
- The captain was sitting with his legs crossed at the time of the movement, which contributed to his legs being trapped against the flight controls.
- Previous corrective measures implemented by the seat and aircraft manufacturers had failed to prevent similar occurrences of this specific switch failure.
- The crew's effective use of Crew Resource Management (CRM) allowed for a rapid recovery of the aircraft's flight path.