The Asiana Airlines jet that crashed at San Francisco airport was traveling much slower than recommended, US investigators said, as the carrier confirmed that the pilot had still been in training.
The flight data recorder showed that as the Boeing 777 approached the runway its pilots were warned that the aircraft was likely to stall and asked to abort the landing.
Seconds later, the plane smashed into the ground, bursting into flames, killing two people and injuring 182 others.
The request to abort the landing was captured on the cockpit voice recorder 1.5 seconds before the plane crashed, National Transportation Safety Board chairwoman Deborah Hersman, who is leading the probe, said on Sunday.
Her announcement came minutes after a video obtained by CNN confirmed that the aircraft, carrying more than 300 people, clipped a seawall short of the airport and skidded on its belly on to the runway.
The footage showed the nose up with the rear of the plane hitting the ground first, before it rolled on to the concrete, abruptly bounced upward and then spun around 180 degrees.
The two passengers who died were teenage Chinese girls.
Asked about the speed at which the plane was traveling, Hersman, whose NTSB team is examining the wreckage, stressed that it was well below the recommended 137 knots.
"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. But again, we are not talking about a few knots here or there. We're talking about a significant amount of speed below 137," she said.
The crash sheared off the plane's landing gear and ripped the tail off. Large portions of the fuselage were burned out in the massive fire that erupted.
The findings came as Asiana said pilot Lee Kang-Kuk, 46, had 43 hours of experience in piloting the 777 and was still undergoing training, although he was had more than 9,000 hours of total flight time under his belt.
"It's true that Lee was on transition training for the Boeing 777", an Asiana spokeswoman told AFP on Monday. However, he was accompanied by an experienced trainer, who acted as co-pilot.
On Sunday, Yoon Young-Doo, the CEO of Asiana Airlines, based in Seoul, said "currently we understand that there are no engine or mechanical problems" with the plane, which was bought in 2006.
NTSB chair Hersman refused to comment on whether the flight crew was at fault, noting that the pilots would be interviewed and stressing that it was day one of the investigation.
However she said the plane's low speed triggered an automatic device called a "stick shaker", which warns pilots that a plane is about to stall. The warning came four seconds before the crash -- 2.5 seconds before one of the pilots tried to abort the landing.
Hersman said: "There was a call out for a go around from one of the crew at 1.5 seconds prior to impact. And the call out is a -- is communication between the crew that they want to go around, that means they want to not land but apply power and go around and try to land again."
Analysts said the pilot's request came far too late.
Asiana Flight 214 originated in Shanghai, and had 307 people on board -- 291 passengers and 16 crew -- after it stopped to pick up passengers in Seoul.
Several of the injured were still in critical condition or unconscious, said the San Francisco General Hospital.
Doctors saw "a huge amount of spine fracture, some of which include paralysis," Margaret Knudson, interim surgery chief at the hospital, told reporters.
Some 15 or 16 had yet to regain consciousness, she said.
The passengers included 141 Chinese nationals, 77 South Koreans and 64 Americans.
In total, 123 people aboard the flight escaped unharmed, US officials said.
The accident sent shares in Asiana tumbling as much as 6.4 percent on Monday, with analysts warning that the disaster could have a long-term negative impact on the firm.
The twin-engine Boeing 777 is one of the world's most popular long-distance planes, often used for flights of 12 hours or more.
It was the first fatal crash involving an Asiana passenger plane since June 1993, when a Boeing 737 operated by the carrier crashed into a mountain in South Korea, killing 68.