A preliminary report from Chile’s aviation authority on the LATAM Airlines plane that plunged mid-air on March 11 says that the captain’s seat experienced an “involuntary movement forward” midflight.

LATAM Flight 800 was flying from Australia to New Zealand when the Boeing 787 Dreamliner descended 400 feet, and the cause of the sudden plunge is yet to be determined, according to the report.

It says crews that worked on the plane during and before the flight have been interviewed, including maintenance personnel that “verified the condition of the captain’s seat.”

Authorities are also studying any history related to the seats inside the plane’s cockpit.

The black box will be handed over to the National Transportation Safety Board (NTSB), and the captain’s seat will be inspected by the FAA and Boeing, the report said.

The sudden drop injured 50 people.

Days after the incident, Boeing sent an advisory to airlines that operate the Boeing 787 Dreamliner recommending they inspect cockpit seat switches on the planes. It has sent a similar notice to airlines in 2017.

This is a developing story and will be updated.