Investigators are trying to understand whether automated cockpit equipment Asiana flight 214's pilots said they were relying on to control the airliner's speed may have contributed to the plane's dangerously low and slow approach just before it crashed.
New details in the accident investigation that were revealed by National Transportation Safety Board Chairman Deborah Hersman were not conclusive about the cause of Saturday's crash. But they raised potential areas of focus: Was there a mistake made in setting the automatic speed control, did it malfunction or were the pilots not fully aware of what the plane was doing?
One of the most puzzling aspects of the crash has been why the wide-body Boeing 777 jet came in far too low and slow, clipping its landing gear and then its tail on a rocky seawall just short the runway. The crash killed two of the 307 people and injured scores of others, most not seriously.
Officials didn't explain fully why the plane approached the notoriously difficult landing strip too low and slow, likely causing the crash, although they did quote testimony from one of the pilots that explained more about what occurred moments before Flight 214 crash landed.
Hersman said the pilot at the controls was only about halfway through his training on the Boeing 777 and was landing at the San Francisco airport for the first time. Hersman also said his co-pilot was on his first trip as a flight instructor.
New information released Wednesday also showed that people did not begin fleeing the aircraft until 90 seconds later when the fire erupted. Officials say the delay occurred as the pilot checked with the tower at the airport.
The NTSB hasn't ruled anyone at fault in the crash, with Hersman saying that probable cause will not be determined on scene.
Audio recordings show the pilots tried to correct the plane's speed and elevation until only seconds before hitting the seawall at the end of the runway, an impact that sent the fuselage bouncing and skidding across the airfield.
The pilots told the National Transportation Safety Board that the auto-throttles were set to maintain 137 knots, which is faster than the plane was travelling at its approach.
In the 777, turning the autothrottle on is a two-step process -- first it is armed then it is engaged, Boeing pilots said.
Choi Jeong-ho, a senior official at South Korea's Ministry of Land, Infrastructure and Transport, said investigators confirmed the auto throttle was in an armed position, and an exact analysis on whether the automatic throttle system worked will be possible after an analysis on the plane's black box.
Hersman didn't say whether the Asiana's autothrottle was engaged.
Bob Coffman, an American Airlines captain who has flown 777s, said the only way he could think of for the Asiana plane to slow as quickly as the NTSB has described would be if the autothrottle had somehow shifted into the idle mode.
"There is no way to get from a normal airspeed and normal position at 500 feet to an abnormally slow airspeed at 300 feet unless there wasn't enough thrust either deliberately or inadvertently," he said.
Here is what is known: Seven seconds before impact, someone in the cockpit asked for more speed after apparently noticing that the jet was flying far slower than its recommended landing speed. A few seconds later, the yoke began to vibrate violently, an automatic warning telling the pilot the plane was losing lift and in imminent danger of an aerodynamic stall. One and a half seconds before impact came a command to abort the landing.
Hersman said at the news conference that the instructor realized the craft was coming in too low by the time the plane went below 500 feet. This was indicated by the Precision Approach Path Indicators (or PAPIs) situated on the runway, which were showing three red lights out of four. A normal approach would show two red lights and two white, with more reds than white indicating the plane is too low, while more whites than red indicate a plane is coming in too high.
By the time Flight 214 reached 200 feet, the PAPI’s were all red, indicating that the aircraft was perilously low, according to the instructor’s reported testimony. He also stated that the auto-throttle had not maintained the necessary speed.
The plane's airspeed has emerged as a key question mark in the investigation. All aircraft have minimum safe flying speeds that must be maintained or pilots risk a stall, which robs a plane of the lift it needs to stay airborne.
If any of the Asiana pilots "saw something out of parameters for a safe landing," they were obligated to speak up, said Cass Howell, an associate dean at the Embry-Riddle Aeronautical University in Daytona Beach, Fla.
"There are dozens and dozens of accidents that were preventable had someone been able to speak up when they should have, but they were reluctant to do so for any number of reasons, including looking stupid or offending the captain," said Howell, a former Marine Corps pilot.
There has been no indication, from verbal calls or mechanical issues, that an emergency was ever declared by pilots. Most airlines would require all four pilots to be present for the landing, the time when something is most likely to go wrong, experienced pilots said.
Investigators want to nail down exactly what all four pilots were doing at all times.
Coroner Robert Foucrault told The San Francisco Chronicle on Tuesday that investigators told the parents of 16-year-old Ye Meng Yuan that she was the girl who may have been been struck and killed accidentally on the runway by a fire truck racing to the scene of the crashed plane.
Ye's parents flew into San Francisco International Airport late Monday along with the parents of the other girl killed in Saturday's crash, Ye's close friend Wang Lin Jia, also 16.
The police department's hit-and-run unit is investigating Ye's death.
The Associated Press contributed to this report