NTSB investigator Bill English and agency Chairwoman Deborah A.P. Hersman… (National Transportation…)
SAN FRANCISCO — The pilots flying the Asiana Airlines jetliner that crashed in San Francisco told federal investigators that an automatic throttle — a system akin to a car's cruise control — had failed to keep the jetliner at the proper speed for landing.
The Asiana pilots said in interviews with the National Transportation Safety Board that they had set the auto-throttles to maintain an air speed of 137 knots. That's a significantly faster speed than the plane actually achieved as it came in for its landing at San Francisco International Airport on Saturday.
As the inquiry entered its fourth day, Deborah A.P. Hersman, chairwoman of the National Transportation Safety Board, said investigators were still trying to verify whether the throttles were properly activated.
The pilots' statements do not resolve the central question of why the Boeing 777's speed and altitude fell so far out of the normal range for landing at SFO before it hit a sea wall and crash-landed. But outside air safety experts said the statements suggest a risky reliance on technology when the flight crew should have been constantly monitoring the airplane's speed.
"Whether it was engaged or not working is almost irrelevant," said Barry Schiff, a former TWA pilot and an air safety consultant. "The big mystery of Flight 214 is why in God's name did these two pilots sit there and allow the air speed to get so low."
Experts said the pilots should have been monitoring the plane's speed every few seconds, and could have manually taken control of the engines at any time.
Auto-throttles, which are connected to an airplane's flight management computers, allow pilots to select the appropriate speed for takeoff, cruising or landing. The devices automatically make corrections if there are deviations from the setting.
Jon Russell, a veteran airline pilot and safety official for the Air Line Pilots Assn. on the West Coast, said the auto-throttle is a valuable tool.
"I don't know what happened. It just doesn't make sense," said Russell, noting that the pilots were very experienced in Boeing aircraft. "The situation deteriorated a lot farther than it should have."
Much of the information released by the NTSB since Saturday morning's crash has focused on the pilots, who were flying too low and slow during their final approach. Two people were killed and 182 were injured as the plane's landing gear and tail struck a seawall at the end of Runway 28L.
Investigators said the plane was flying 30 knots under its target landing speed of 137 knots, or almost 158 mph, and had dipped well below the normal flight path into the airport.
Several seconds before the crash landing, a stall warning went off in the cockpit. With the impact 1.5 seconds away, the pilots finally attempted to accelerate and abort the landing, investigators said.
The Asiana pilots were making a visual approach to San Francisco without the instrument landing system, a part of which was not operating due to airfield renovations. NTSB officials said, however, that there were other automated systems and visual references available to assist the flight crew.
At the time, the pilot, Lee Kang-kook, who had only 35 hours flying Boeing 777s, was being checked out and supervised in the plane by Lee Jung-min, a captain who had been certified as a training pilot June 15, less than a month before the crash. It was Lee Kang-kook's first landing in San Francisco in a Boeing 777 and Lee Jung-min's first landing at the airport in a training situation.
Hersman said that when the jetliner crashed, three pilots were in the cockpit. Lee Kang-kook was in the left-hand or captain's seat. Lee Jung-min was in the right-hand or co-pilot's seat, supervising his flight, and a relief first officer was sitting in the jump seat to monitor the landing.
The approach to San Francisco International Airport is not particularly difficult, but it does require closely monitoring a jetliner's air speed as it executes a sweeping 180-degree counterclockwise turn in the approach from the north, according to Robert Ditchey, former vice president for operations at US Airways.
Ditchey said that only the pilot in the left-hand seat — in this case, one who was not yet fully qualified to land the 777 — could see the runway during the turn. The supervising pilot in the right-hand seat could not see the runway from his position, he said.
Aviation safety experts and federal investigators have questioned why the crew did not recognize the problem and take action before the plane struck the end of the runway.
Hersman rejected the suggestion that any problem or misunderstanding about the auto-throttle by the crew would excuse the pilots from their duty to manually fly the airplane.