The Asiana Airlines Boeing 777 was traveling at 106 knots upon impact, far below the recommended approach speed of 137 knots, National Transportation Safety Board Chairwoman Deborah Hersman told reporters Monday.
The jet's engines were increasing from 50 percent capacity 3 seconds before the crash, Hersman told CNN.
The pilots of the jetliner came in "too low, too slow," one expert said earlier, and another said they "have a lot of explaining to do."
Flight 214 from Seoul crash-landed at San Francisco's airport Saturday, killing two teenage passengers and injuring scores of other passengers and crew members.
Federal investigators said Sunday the Boeing 777's throttles were set to idle and the aircraft, with 307 passengers and crew aboard, was traveling so slowly it nearly stalled before it came down, the San Francisco Chronicle reported. The National Transportation Safety Board's preliminary review of the aircraft's flight data and cockpit communications found the veteran pilots tried to abort the landing 7.5 seconds before the crash-landing, the newspaper said.
Hersman earlier told reporters it was premature to say what caused the crash, the Chronicle said.
"Everything is on the table right now," she said.
Airline officials in Seoul ruled out engine problems, the newspaper said. Weather was not believed to have been a factor, either.
Barry Schiff, a former pilot for TWA who has written extensively about aviation safety, told the newspaper pilots "should always make an approach with power, and they didn't do that."
"These pilots have a lot of explaining to do," Schiff said.
Jim Tilmon, a former commercial pilot and aviation consultant in Arizona, said it appeared the crew tried to power up the jetliner's engines but fell "behind the power curve."
"It sounds like, too low, too slow, too late," Tilmon said.
Meanwhile, investigators were trying to determine whether one of the two 16-year-old girls who died when they were ejected from the plane was struck by a responding fire rig, the Chronicle said.