SAN FRANCISCO -- Despite the wealth of details released this week, a top federal air safety official said Thursday that it will be months before a final conclusion is reached on the cause of the Asiana Flight 214 crash at San Francisco International Airport.

In her final briefing to reporters before heading back to Washington, D.C., National Transportation Safety Board Chairwoman Deborah Hersman seemed to rule out mechanical error, intensifying the focus on the pilots.

But after a week of remarkably candid press briefings, Hersman made clear investigators still "have a lot of information to review."

She referred to the crash as "a very significant event. There's a lot of interest in it and we want to make sure that we complete this investigation as expeditiously as possible."

A typical NTSB investigation takes a year to 18 months to determine what -- or who -- caused the plane to crash. But Hersman hopes to have the investigation finished sooner, although she wouldn't provide a more precise timeline.

Late Thursday, crews were scheduled to begin carving up and removing the carcass of the Boeing 777 from the airport's runway 28 Left. Some pieces of the aircraft, including the emergency evacuation slides that deployed inside the cabin, will be sent back to Washington, while other parts will be stored in a secure hangar in the Bay Area.

Hersman said SFO officials "want that airport open. So I want you to know that they've put pressure on us, but they have not pressured in a way that forced us not to get our job done and we very much appreciate that."

Two 16-year-old girls from China were killed and 182 people were sent to hospitals Saturday morning when the tail of their plane slammed into the runway sea wall while landing at the airport after a more than 10-hour flight from Seoul, South Korea, immediately shutting two of SFO's four runways and triggering a chain reaction that diverted air traffic across California and other parts of the country in the days that followed.

Hersman released new details of the investigation so far:

  • On Wednesday, Hersman told reporters that the "flying pilot" in the left seat told investigators that he was temporarily blinded by a "flash of light'' while landing. But on Thursday, she seemed to discount the importance of the flash, saying the pilot "stated he did not believe it affected his vision and he was able to see the cockpit instruments."

    Cockpit voice recordings captured no discussions about the light "or of the flying pilot seeing the light," Hersman said. "Neither of the other two flight crew members mentioned this light during our interviews." Hersman said the light may have been a reflection of the sun.

  • The pilots -- a veteran making his inaugural landing into SFO in a Boeing 777 and his rookie trainer sitting to his right -- had 10 miles of clear visibility.

  • In response to South Korean media reports that air traffic controllers had a shift change 30 seconds before the crash, Hersman said the flight crew "received their final landing clearance 90 seconds prior to impact." When the plane crash-landed, "the tower actually called for the emergency and the emergency vehicles prior to the flight crew calling the tower for an emergency."

  • There was no indication that passengers had activated any personal electronic devices that may have interfered with the plane's landing.

  • The pilots did not "set the aircraft for an auto-land situation. ... They had been cleared for a visual approach and they were hand-flying the airplane."

  • "During the approach there were statements made in the cockpit first about being above the glide path, then about being on the glide path, then later reporting about being below the glide path. All of these statements were made as they were on the approach to San Francisco."

  • Three seconds before the crash, someone in the cockpit called for the plane to abort the landing, or "go around." Then, 1.5 seconds before impact, a different crew member again called for a "go around."

  • The plane's two Pratt & Whitney engines and flight controls appeared "to be responding as expected. ... There is no anomalous behavior of the autopilot, of the flight director and of the auto throttles."

  • The fuel tanks were not breeched. "We don't see a fuel-fed fire," Hersman said.

  • One of the first firefighters to enter the crippled cabin told investigators that the back of the plane suffered significant structural damage, but the seats in the front of the plane "were almost pristine" -- before the interior burst into flames.

    SFO officials will wait until the NTSB's investigation is complete before releasing 911 tapes. But Wednesday night the California Highway Patrol released its 911 calls of people reporting the crash and its aftermath.

    A woman's voice in the background of one call made by a hiker can be heard saying, "Where the hell's the fire engines?"

    Another told dispatchers, "There is a woman out here on the ... runway who is pretty much burned very severely on the head, and we don't know what to do. ... She is severely burned, and she will probably die soon if we don't get any help."

    As the dispatcher reassured the woman that ambulances were on the way, the woman reiterated her fears the victim would die, and she didn't know what to do.

    "Is there any way we can help in any way?" she asked.

    Another caller said she had been on the tarmac for at least 20 minutes and pleaded for medical attention.

    "We've been on the ground for 20 minutes to a half-hour," said the woman, who identified herself as Cindy Stone. "We're almost losing a woman here, we're trying to keep her alive."

    Staff writers Eric Kurhi and Katie Nelson contributed to this report. Contact Dan Nakaso at 408-271-3648. Follow him at Twitter.com/dannakaso.