An Asiana jetliner from Seoul, South Korea, crashed while landing Saturday at San Francisco International Airport, the Federal Aviation Administration said. Pieces of the airplane broke off as it careened down the runway.
The jetliner, Flight 214 from Seoul’s Incheon airport, carried 291 passengers and 16 crew members, the airline said. It was unclear how many on board might have been injured or killed, though many passengers were seen scrambling down inflated escape chutes. The crash was the first in the United States since February 2009.
Smoke billowed out of holes in the fuselage of the Boeing 777 as firefighters rushed to the wreckage on the runway. Aircraft parts were scattered across the tarmac — the plane’s wheels, tail and one engines were ripped off.
“I looked up out the window and saw the plane coming in extremely fast and incredibly heavy,” said Isabella Lacaze, 18, from Fort Worth, who witnessed the crash from the San Francisco Airport Marriott Waterfront.
“It came in at a 30- or 45-degree angle and the tail was way, way lower than the nose,” said another witness, Stefanie Turner, 32, from Arizona.
The plane clipped something as it touched down near the sea wall, Ms. Lacaze said. “And then it hit one of the planes that was already on the runway.”
The plane that was hit said United on its side, she said, but did not appear to sustain much damage. Other witnesses were unsure whether the Asiana plane had hit another aircraft.
“I remember watching the nose go to the ground and the tail way up in the air and then the tail back to ground hard,” Ms. Lacaze said, describing the plane careening out of control. At that point the tail snapped off and the rest of the plane skidded down the runway.
“The smoke was not bad at all at first,” she said. “It was like one cloud. It took maybe a minute or two for the chutes to come out of the side,” and people began to pour out almost immediately.
David Eun, who said in a Twitter message that he had been a passenger on the plane, posted a picture of a downed Asiana jetliner from ground level that showed some passengers walking away from the aircraft.
An aviation official who did not want to be identified said that the plane was not making an emergency landing and that the situation had been entirely routine until the crash. The cause was unclear.
Arnold Reiner, a retired airline captain and the former director of flight safety at Pan Am, said that it appeared from television images that the jetliner had touched down far earlier than the normal landing point, which is about 1,000 feet down the runway. That runway, 28 Left, has a “displaced threshold,” he said, meaning that the runway’s usable area does not begin at the start of the pavement. The Instrument Landing System would normally guide the pilot to the proper touchdown point, but in clear weather, pilots will sometimes fly a visual approach.
If the plane touched down too soon, before the paved area or before the area intended for landings, it might have torn off its landing gear, he said, and begin to skid along on its engine cowlings. “At that point, all bets are off,'’ he said, and the tail might have hit the ground with more force than the fuselage was intended to handle.
One question for investigators, Mr. Reiner said, is who was at the controls. The 777 has a two-pilot cockpit but on a flight that long, there is typically a “relief pilot” or two on board, so no one has to work continuously for the entire flight.
Steven B. Wallace, who was the director of the office of accident investigation at the F.A.A. from 2000 to 2008, said that “it seems clear that the airplane hit short of the runway.”
“Why that happened, I don’t know,” he said. Mr. Wallace, who is a licensed commercial pilot, said the pilot could have made a mistake and come in too low or there could have been wind shear.
Even though the runway stretches to the sea wall, planes normally would not touch down until they had passed gold markings a safe distance down the runway. But videos show significant debris between the markings and the sea wall, he said.
The runway is 11,381 feet long and 200 feet wide. The designation 28 for the runway indicates that the plane was landing toward the west.
The 777 has an exceptionally capable flight data recorder, one of the two “black boxes” on the plane, which could quickly provide important details.
The last few years have been an exceptionally safe period for airline travel in the United States. The last crash was in February 2009, when a twin-engine Continental turboprop approaching Buffalo on a flight from Newark crashed into a house about five miles from the airport. All 44 passengers and the crew of four died, along with one person on the ground.
Korean carriers have historically had more difficulty.
In August 2001, the Federal Aviation Administration froze service from Korean carriers coming into the United States, limiting them to the schedules and aircraft they were then flying, because it considered safety regulation by the South Korean government inadequate. The restrictions were later lifted.
In December, 1999, a Korean Airlines 747 cargo jet crashed near London. In August, 1997, a Korean Air 747 came in short of the runway in Guam, killing 228 people.
Asiana Airlines, established in 1988, is based in South Korea and also flies to Los Angeles, Seattle, Chicago and New York, in addition to various destinations in Europe, the Russian far east, China, Southeast Asia and elsewhere. It operates 12 Boeing 777 extended-range aircraft, according to its Web site, and offers suites for first-class passengers with what is described as the world’s largest television screens for individual travelers.