US investigators say the Boeing 777 that crash-landed at San Francisco airport on Saturday was "significantly below" its target speed near the runway, and the pilot tried to abort the landing.
They say the pilot of the Asiana Airlines flight from Seoul requested a "go around" one and a half seconds before the crash, the BBC reports.
The plane with 307 people aboard crashed short of the runway, killing two people and injuring dozens. It apparently hit a seawall, ripping off its tail.
Asiana has confirmed the two passengers who died were female Chinese teenagers who had been seated at the back of the aircraft. They are believed to be the first fatalities in a Boeing 777 crash.
The BBC reports air safety officials are looking into the possibility rescue crews ran over one of them.
At a news conference on Sunday, National Transportation Safety Board chief Deborah Hersman said aircraft speed was below the planned 137 knots (254km/h) as the plane approached the runway.
Citing data both from the cockpit voice recorder and flight data recorder, she said there was a call to boost the speed about two seconds before the impact. The pilot then requested a "call to go around" and not land.
"We have to take another look at the raw data and corroborate it with radar and air traffic information to make sure we have a very precise speed," Ms Hersman said. "But again, we are not talking about a few knots here or there. We're talking about a significant amount of speed below 137."
Chief pilot training on 777
The South Korean airline says the pilot in charge of landing the Boeing 777 was training for the long-range plane, Reuters reports. An Asiana spokesperson says it was pilot Lee Kang-kook's maiden flight to the airport with that particular jet even though he was a veteran.
Bowing in front of TV cameras at a Seoul news conference, Asiana head Yoon Young-doo apologised "deeply" for the effect the accident had had on all those involved, reports the BBC. He said there was no emergency alarm and the crew had made the usual requests to passengers to fasten their seatbelts to prepare for landing.
"Currently we understand that there were no engine or mechanical problems," he said.