Chilean investigators have determined that an involuntary forward shift of the captain’s seat preceded the in-flight upset involving a LATAM Airlines Boeing 787-9 last month.

The aircraft had been cruising at 41,000ft en route to Auckland from Sydney on 11 March.

It experienced a “sudden unintentional” loss of altitude, says Chilean aeronautical directorate DGAC, at about 02:30UTC while around 320nm west of Auckland.

The aircraft descended some 400ft but the crew recovered without exceeding load limits for the twinjet.

But the incident injured 13 occupants – 10 passengers and three cabin crew – with three of them needing hospital treatment.

Simulation LATAM 800-c-Chilean DGAC

Source: Chilean DGAC

Investigators have reconstructed the upset which involved a sudden 400ft descent

Flight LA800 had been carrying 263 passengers and nine crew members.

“The seat on the left side of the cockpit, with the captain in his position, began an involuntary movement forward,” says the inquiry.

Investigators have not determined the reason for the movement of the captain’s seat, but state that there were no adverse weather conditions or turbulence affecting the aircraft.

Seat video LATAM 787-c-Chilean DGAC

Source: Chilean DGAC

Video of position-adjust switch and cover behind the captain’s (left pair) and first officer’s (right pair) seat

But the inquiry has recorded video footage of the back of each pilot’s seat, where a switch to adjust the seat’s position is located and normally accessed by lifting a cover.

The switch cover for the captain’s seat appears not to be lying flush with its surround, in contrast to that on the first officer’s seat – although the inquiry has not remarked on the relevance of the video to the circumstances.

Chilean investigators are sending the flight-data recorder and cockpit-voice recorder to the US National Transportation Safety Board for analysis, and will liaise with Boeing and the US FAA regarding a physical inspection of the captain’s seat.