On March 11, dozens of people were injured when Latam Flight LA800 suddenly lost altitude and tossed crew and passengers around the cabin and into the ceiling.

The flight had been taking 272 passengers from Sydney to Auckland when the incident occurred, prompting a major emergency service response.

An initial report suggested accidental cockpit seat movement caused the aircraft to plunge, and Boeing instructed airlines to check pilot seats on 787 Dreamliner jets were covered.

Now, a new report released by Chile’s Directorate General of Civil Aviation proves this was what happened.

The report states the left-side seat “began an involuntary forward movement” while the captain was in position. However, turbulence and weather “were not causal or contributing factors in the operation”.

The black box and pilot seat are in Chile, but will be sent to the United States. Once there, the National Transportation Safety Board will inspect the black box while the Federal Aviation Administration and Boeing will inspect the seat, CNN reported.

One question yet to be answered is how exactly the seat began involuntary forward movement. One theory, proposed by the Wall Street Journal, is that a flight attendant hit a switch on the pilot’s seat while delivering a meal. This released the seat forward, pushing the pilot into the control panel and prompting the plane to dive.

A passenger on the flight, Priscilla Waller-Subritzky, told the Herald she was watching a movie when the plane lost altitude and “a number of passengers and crew were thrown into the roof of the plane”.

Initially, she “went into fight mode” and started helping where she could because the crew were injured. However, when the adrenalin wore off, she experienced a lot of pain and headed for the emergency department.

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Fourteen Hato Hone St John units arrived at the airport to deal with the injuries.

Latam initially described the incident as a “technical issue”. In response, several aviation experts said it was an example of why passengers should have their seatbelts fastened at all times during a flight unless moving around the cabin.

Writing in the Sydney Morning Herald, David Evans, who worked as a Qantas pilot for 37 years, said the damage was magnified by people not wearing seatbelts.

“No one would ever wish to criticise an injured person. But with the exception of busy crew members, if the passengers on board the Dreamliner turned nightmare-liner had been strapped in, we probably wouldn’t be talking about this,” he wrote.