Investigators found that two key navigation parts failed on a United Airlines flight from Lagos to Washington on January 24, causing the plane to lurch suddenly and injure several passengers.

The National Transportation Safety Board said the left and then right inertial reference units failed on the Boeing 787 jetliner, which was followed by the autopilot disconnecting automatically and sudden altitude changes. There were 16 injuries, including one serious injury. The flight returned to Nigeria.

United declined to comment. Boeing did not immediately comment.

The safety board said the flight movements lasted for 12 minutes at 36,000 feet (11,000 meters) over Côte d’Ivoire. At the time, flight attendants were serving meals in the cabin.

Investigators removed the flight recorders and other equipment from the aircraft in Lagos and sent them to Washington for the safety board to inspect. REUTERS