The pilot had nearly 10,000 hours flying other planes but only 43 in the 777, a plane he still was getting used to flying, according to an airline spokesperson.

The pilot at the controls of an Asiana plane that crash landed was guiding a Boeing 777 into the San Francisco airport for the first time, and tried but failed to abort the landing after coming in too slow to set down safely, aviation and airline officials said on Sunday.

It was unclear if the pilot’s inexperience with the aircraft and airport played a role in Saturday’s crash. Officials were investigating whether the airport or plane’s equipment could have also malfunctioned.

Further, San Mateo County Coroner Robert Foucrault said on Sunday that he was investigating whether one of the two teenage passengers killed Saturday actually survived the crash but was run over by a rescue vehicle rushing to aid victims fleeing the burning aircraft.

Remarkably, 305 of 307 passengers and crew survived the crash and more than a third didn’t even require hospitalization. Only a small number were critically injured.

Deborah Hersman, head of the National Transportation Safety Board, said the slow speed of Flight 214 in the final approach triggered a warning that the jetliner could stall, and an effort was made to abort the landing but the plane crashed barely a second later.

At a news conference, Ms. Hersman disclosed the aircraft was travelling at speeds well below the target landing speed of 137 knots per hour, or 157 mph.

Seven seconds before the crash, pilots recognized the need to increase speed, she said, basing her comments on an evaluation of the cockpit voice and flight data recorders that contain hundreds of different types of information on what happened to the plane. Three seconds later, the aircraft’s stick shaker — a piece of safety equipment that warns pilots of an impending stall — went off. The normal response to a stall warning is to boost speed, and Ms. Hersman said the throttles were fired and the engines appeared to respond normally.

At 1.5 seconds before impact, there was a call from the crew to abort the landing.

The details confirmed what survivors and other witnesses said they saw — an aircraft that seemed to be flying too slowly just before its tail apparently clipped a seawall at the end of the runway and the nose slammed down.

Pilots normally try to land at the target speed, in this case 137 knots, plus an additional five more knots, said Bob Coffman, an American Airlines captain who has flown 777s. He said the briefing raises an important question- “Why was the plane going so slow?”

The plane’s Pratt & Whitney engines were on idle and the pilots were flying under visual flight rules, Ms. Hersman said. Under visual flight procedures in the Boeing 777, a wide-body jet, the autopilot would typically have been turned off while the automatic throttle, which regulates speed, would been on until the plane had descended to 500 feet in altitude, Mr. Coffman said. At that point, pilots would normally check their airspeed before switching off the auto-throttle to continue a “hand fly” approach, he said.

There was no indication in the discussions between the pilots and the air traffic controllers that there were problems with the aircraft.

The airline said on Monday in Seoul that the pilot at the controls had little experience flying that type of plane and was landing one for the first time at that airport.

Asiana spokeswoman Lee Hyomin said that Lee Gang-guk, who was at the controls, had nearly 10,000 hours flying other planes but only 43 in the 777, a plane she said he still was getting used to flying. Another pilot on the flight, Lee Jeong-min, had about 12,390 hours of flying experience, including 3,220 hours on the 777, according to the Ministry of Land, Infrastructure and Transport in South Korea. Mr. Jeong-min was the deputy pilot, tasked with helping Mr. Gang—guk get accustomed to the 777, according to the airline.

The flight originated in Shanghai, China, and stopped over in Seoul, South Korea, before making the nearly 11-hour trip to San Francisco. The South Korea-based airline said four South Korean pilots were on board, three of whom were described as “skilled.”

Among the travellers were citizens of China, South Korea, the United States, Canada, India, Japan, Vietnam and France. There were at least 70 Chinese students and teachers heading to summer camps, according to Chinese authorities.

Authorities immediately closed the airport and rescuers rushed to the scene. A United Airlines pilot radioed the control tower, saying, “We see people ... that need immediate attention. They are alive and walking around.”

“Think you said people are just walking outside the airplane right now?” the controller replied.

“Yes,” answered the pilot of United Flight 885. “Some people, it looks like, are struggling.”

At the crash scene, police officers provided knives to crew members inside the burning wreckage so they could cut away passengers’ seat belts. Passengers jumped down emergency slides, escaping from billowing smoke that rose high above the bay. Some passengers who escaped doused themselves with water from the bay, presumably to cool burns, authorities said.

By the time the flames were out, much of the top of the fuselage had burned away. The tail section was gone, with pieces of it scattered across the beginning of the runway.

Mr. Foucrault, the coroner, said senior San Francisco Fire Department officials notified him and his staff at the crash site on Saturday that one of the 16-year-olds who was killed may have been struck on the runaway. He expects the autopsy — to be completed by Monday — will involve determining whether the girl’s death was caused by injuries suffered in the crash or “a secondary incident.”

Mr. Foucrault said one of the bodies was found on the tarmac near where the plane’s tail broke off when it slammed into the runway. The other was found on the left side of the plane about 30 feet away from where the jetliner came to rest after it skidded down the runway.

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