A burned Asiana Airlines Inc. plane sits on the runway after it crashed landed at San Francisco International Airport (SFO) in San Francisco, California, U.S., on Saturday, July 6, 2013. A Boeing Co. 777 operated by Asiana Airlines Inc. on a flight from Seoul crashed while landing at San Francisco International Airport, killing two and burning as passengers plummeted down emergency slides. Photographer: David Paul Morris/Bloomberg via Getty Images
(NBC NEWS) -- Federal investigators said Monday they hope to learn much more from interviews with the four pilots aboard the jetliner that crash-landed at the San Francisco airport, and they said the aircraft was still 500 feet in the air - much too high - when it slowed to touchdown speed.
Two days after Asiana Airlines Flight 214 scraped across the runway and caught fire, killing two teenagers and injuring 180 passengers, the investigators gave no indication of mechanical or external problems, suggesting the cockpit holds vital clues.
"We're looking at what they were doing, and we want to understand why they were doing it," said Deborah Hersman, head of the National Transportation Safety Board. "We want to understand what they knew and what they understood."
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She told reporters she hoped to have much more detail about the crash on Tuesday, after the interviews with the four pilots. The plane crossed the Pacific Ocean from Seoul, South Korea, and transoceanic flights often have extra pilots.
Investigators will look to make sure the crew understood the automated equipment on the aircraft, a Boeing 777, and will also look for signs of fatigue, illness or other health problems. Asiana said Monday that the captain was still training on the 777 and was landing one at San Francisco International for the first time.
The plane apparently clipped a seawall before reaching the tarmac. Pieces of the plane were found among the rocks of the seawall and in the waters of San Francisco Bay, Hersman said.
Hersman also revealed a detailed timeline showing that the plane had already slowed below its target speed for landing when it was at 500 feet more than 30 seconds from touching down. Moments before landing, the plane had slowed to about 119 mph - roughly 40 mph slower than it should have been going.
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Investigators said Sunday that the plane's "stick shaker" function, which physically rattles the manual controls to alert the pilot to a possible stall, activated with four seconds left in the flight.
By that point, there was little the pilots could do, aviation experts told NBC News. During a stall at higher altitudes, pilots are supposed to add power and point the nose of the plane down in order to pick up airspeed and stabilize the plane.
But with four seconds to go, pointing the nose down would have meant hitting the runway with it, and in any case there was not enough time left to gun the engines to full power for stability, the experts said.
"He was simply too low," said J.F. Joseph, a retired Marine colonel who has been involved in hundreds of aircraft accident and incident investigations. "He ran out of airspeed, altitude and ideas at the same time. You're simply out of options."
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Hersman said, however, that published reports suggesting the plane was dropping at 4,000 feet per second were false, and that there was no evidence of an "abnormally steep descent."
The two teenagers killed were Chinese girls on their way to summer camp in the United States. Authorities are investigating whether a fire truck ran over one of them as it raced to help. They gave little information on that probe Monday, but they did say the girls were seated toward the back of the plane.
"This is an area of the aircraft that was structurally significantly damaged," Hersman said. "It's an area where we're seeing a lot of the critical of serious injuries."
The deaths were the first in the 18 years that the 777 has been in service.
As the investigation moved forward, police and firefighters who were part of the emergency response described what they said was a surreal scene as they helped the last passengers to safety and put out the fire on board.
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They described members of the Asiana crew begging officers to toss them knives so they could free passengers. Police Lt. Gaetano Caltagirone recalled seeing his partner, Officer Jim Cunningham, tearing away parts of the plane to widen an exit for rescues.
"He's handing me seat panels. We're throwing them outside," he said. "There was so much chaos going on, and it was quiet. Everybody was doing what they were trained to do - save lives. And way beyond."
Fire Lt. Christine Emmons said she and her partner ran up one of the plane's inflatable emergency chutes and finding four trapped passengers. Black smoke in the cabin thickened as the passengers were freed.
Asiana identified the pilot as Lee Kang-kuk and said he had logged 43 hours flying the 777 over nine flights. It takes 60 hours and 10 flights to be considered fully qualified, the airline told NBC News. When a pilot learns a new type of aircraft, the status before full qualification is known as transition training.
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Lee had 9,700 hours of experience flying other jetliners - the Airbus A320 and the Boeing 737 and 747, Asiana said. The co-pilot had more than 3,000 hours on the 777, a twin-engine, wide-body jet, the airline said.
Asked on TODAY whether the pilot's inexperience landing the 777 at that airport might have been a factor, Hersman said investigators would consider it, but she added that it's not unusual for pilots to make their first landing at an airport.
"They fly all around the world. There are a lot of different destinations," she said. "What you want to do is have a crew that's proficient in the aircraft and works together well, that you have good crew pairings. That's important."
Reuters and The Associated Press contributed to this report.
By Erin McClam and Julie Yoo, NBC News