While federal investigators began piecing together what led to the crash, San Mateo County Coroner Robert Foucrault disclosed that he was looking into the possibility that one of the two teenage passengers who died Saturday actually survived the crash but was run over by a rescue vehicle rushing to aid victims as the plane burst into flames. Remarkably, 305 of 307 passengers survived the crash and more than a third didn’t even require hospitalization. Only a small number were critically injured.
Accident investigators are trying to determine whether pilot error, mechanical problems or something else was to blame for the crash. At a news conference, NTSB chief Deborah Hersman disclosed the Boeing 777 was traveling at speeds well below the target landing speed of 137 knots per hour, or 157 mph.
“We’re not talking about a few knots,” she said.
Hersman described the frantic final seconds of the flight as the pilots struggled to avoid crashing.
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 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, Hersman said. The normal procedure in the Boeing 777, a wide-body jet, would be to use the autopilot and the throttle to provide power to the engine all the way through to landing, Coffman said.
There was no indication in the discussions between the pilots and the air traffic controllers that there were problems with the aircraft.
Among the questions investigators are trying to answer was what, if any, role the deactivation of a ground-based landing guidance system due to airport construction played in the crash. Such systems help pilots land, especially at airports like San Francisco where fog can make landing challenging. Conditions Saturday were almost perfect, with sun and light winds.
The flight originated in Shanghai, China, and stopped in Seoul, South Korea, before making the almost 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.”