The Asiana Airlines Boeing 777 that crashed at San Francisco’s airport on Saturday was traveling “significantly below” its intended speed and its crew tried to abort the landing just seconds before it hit the seawall in front of the runway, the U.S. National Transportation Safety Board said on Sunday.

Information collected from the plane’s cockpit voice recorder and flight data recorder indicated that there were no signs of trouble until seven seconds before impact, when the crew tried to accelerate.

Two teenage Chinese girls on their way to summer camp in the United States were killed and more than 180 injured in the crash, the first fatal accident involving the Boeing 777 since it entered service in 1995.

The pilot of the crashed Asiana plane at San Francisco airport was still “in training” for the Boeing 777 when he attempted to land the aircraft under supervision on Saturday, the South Korean airline said.