Five seconds later, at 50 percent power, speed began to increase.
A key question raised by the NTSB's account is why two experienced pilots — the pilot flying the plane and another supervising pilot in the other seat — apparently didn't notice the plane's airspeed problem.
Part of the answer to that question may lie in whether the pilot flying, after switching off the autopilot, still had the plane's autothrottle engaged during the descent.
Aviation safety experts have long warned that an overreliance on automation is contributing to an erosion of pilots' stick-and-rudder flying skills. It's too soon to say if that was the case in the Asiana crash, but it's something NTSB investigators will be exploring, they said.
"It sounds like they let the airplane get slow and it came out from under them," said John Cox, a former US Airways pilot and former Air Line Pilots Association air crash investigator.
"There are two real big questions here: Why did they let the airplane get that slow, and where was the non-flying pilot, the monitoring pilot, who should have been calling out 'airspeed, airspeed, airspeed,' " Cox said.
More than 180 people aboard the plane went to hospitals with injuries. But remarkably, 305 of 307 passengers and crew survived, and more than a third didn't even require hospitalization. Only a small number were badly hurt.
The passengers included 141 Chinese, 77 South Koreans, 64 Americans, three Canadians, three Indians, one Japanese, one Vietnamese and one person from France. Asiana President Yoon Young-doo planned to leave for San Francisco later Tuesday to visit hospitalized passengers, according to Asiana spokeswoman Lee Hyomin.
Twenty-three South Koreans have so far left for San Francisco to visit their injured family members and relatives since the crash, according to South Korea's Ministry of Land, Infrastructure and Transport.
After the crash, three firefighters — and two police officers without safety gear — rushed onto the plane to help evacuate trapped passengers, including one who was trapped under a collapsed bulkhead.
They had gotten everyone off the craft except one elderly man, who was in his seat, moaning and unable to move.
"We were running out of time," San Francisco Fire Department Lt. Dave Monteverdi recalled Monday at a news conference. "The smoke was starting to get thicker and thicker. So we had no choice. We stood him up and amazingly, he started shuffling his feet. That was a good sign...we were able to get him out and he was pretty much the last person off the plane."
The two dead passengers were identified as 16-year-old students from China who were scheduled to attend summer camp in California with dozens of classmates.
One of their bodies was found on the tarmac near where the plane's tail broke off when it slammed into the runway, the other was found on the left side of the plane about 30 feet (10 meters) away from where the jetliner came to rest after it skidded down the runway.
The flight originated in Shanghai, China, and stopped over in Seoul, South Korea, before making the nearly 11-hour trip to San Francisco.
NTSB investigators are also sure to examine whether pilot fatigue played a role in the accident, which occurred after a 10-hour nighttime flight. As is typical for long flights, four pilots were aboard, allowing the crew to take turns flying and resting. But pilots who regularly fly long routes say it's difficult to get restful sleep on planes.
The accident occurred in the late morning in San Francisco, but in Seoul it was 3:37 a.m.
"Fatigue is there. It is a factor," said Kevin Hiatt, a former Delta Air Lines chief international pilot. "At the end of a 10-hour flight, regardless of whether you have had a two-hour nap or not, it has been a long flight."