After nearly 11 hours in the air, the passengers travelling from Seoul to San Francisco were looking forward to a quick and uneventful landing as Asiana Airlines Flight 214 approached the airport from over San Francisco Bay. What they got instead, without a word of warning, was terror, panic and confusion.

The Boeing 777 slammed into the runway on Saturday morning, breaking off its tail and catching fire before slumping to a stop that allowed the lucky ones to flee down emergency slidesBy the time the 307 people on the flight all were accounted for several hours later, two Chinese teenage girls found outside wreckage had been confirmed dead and 182 transported to area hospitals. One passenger, Benjamin Levy (39), said it looked to him that the plane was flying too low and too close to the bay as it approached the runway. A Fire Department official said the two who died were found on “the exterior” of the plane. “Having surveyed that area, we’re lucky that there hasn’t been a greater loss,” she said.

An airport spokesman said 49 people were critically injured and 132 had less significant injuries.

The flight originated in Shanghai, China, and stopped over in Seoul before coming to San Francisco, officials said. The airline said there were 16 crew members aboard and 291 passengers. Thirty of the passengers were children.

Asiana President Yoon Young-doo told it would take time to determine the cause but ruled out the possibility of mechanical problems.He said the plane was bought in 2006.

Based on witness accounts in the news and video of the wreckage, Mike Barr, a former military pilot and accident investigator , said it appeared the plane approached the runway too low and something may have caught the runway lip — the seawall at the end of the runway. San Francisco is one of several airports around the country that border bodies of water that have walls at the end of their runways to prevent planes that overrun a runway from ending up in the water.

Since the plane was about to land, its landing gear would have already been down, Mr. Barr said. It’s possible the landing gear or the tail of the plane hit the seawall, he said. If that happened, it would effectively slam the plane into the runway, he said.

Mr. Barr said he could think of no reason why a plane would come in to land that low.

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