Three Indian nationals were among the 305 survivors of the crash that killed two Chinese girls and left 49 seriously hurt.
The Boeing 777's voice and flight data recorders show that the flight from South Korea was coming in too slow and too low and that the pilots appear to have increased speed seven seconds before impact, the head of the US National Transportation Safety Board Deborah Hersman said Sunday.
A stall warning sounded four seconds before the crash, and the crew then made an internal decision "to initiate a go-around 1.5 seconds to impact," she was quoted by CNN as telling reporters in San Francisco.
The NTSB's preliminary assessment of the plane's cockpit and flight data recorders appear to indicate that the flight went from a routine landing to a disaster in a matter of seconds.
But when asked if pilot error was to blame, Hersman said the crash landing was still under investigation.
"I would discourage anyone from drawing any conclusions at this point," she said, adding that investigators are still working to corroborate the information on the recorders.
"What we need to do is corroborate the information we have both on the flight data recorder and the cockpit voice recorder," Hersman said.
The target air speed for the approach of the flight was 137 knots, and the crew can be heard on the cockpit voice recorder acknowledging the speed, Hersman said.
But the speed was significantly below 137 knots, and "we are not talking about a few knots," she said.
Hersman said her team plans to interview the pilots in the coming days. The pilot sitting in the captain's seat had 43 hours of experience flying the B777-200, CNN reported citing Choi Jeong-ho, the head of the South Korea's Aviation Policy Bureau. He was identified as Lee Kang-gook, he said.
Internal damage to the plane is "really striking," Hersman said, and officials are thankful there weren't more deaths.
In all, 182 people were hospitalised with injuries ranging from paralysis to "severe road rash" and 123 others walked away from the crash landing.
At San Francisco General, 17 survivors remained hospitalised, six of them in critical condition.