SAN FRANCISCO -- The top federal investigator probing the crash of a plane at San Francisco International Airport said Wednesday that it's too early to blame the pilots for the tragedy.
"At this point in the investigation, we are not reaching any conclusions," Deborah Hersman, chairwoman of the National Transportation Safety Board, told CNN. "We're gathering factual information. We know a lot, and what we need to do is correlate all that information. We need to put it together and see what it tells us."
The pilots flying the Asiana Airlines jetliner 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, or about 158 mph. Investigators have said that when the plane came in for landing it was flying 30 knots below that target landing speed and had dipped well below the normal flight path into the airport.
Hersman 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 the plan struck a sea wall and crash-landed Saturday morning's crash, killing two people and injuring 182.
Outside air-safety experts said the pilots' 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."
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.
"But let me be clear: the crew is required to maintain a safe aircraft, which means that they need to monitor. They have a monitoring function, all three of them in the cockpit. One of the very critical things that need to be monitored on approach to landing is speed," she said.
None of the crew was tested for drugs or alcohol after the crash, Hersman said, because foreign flight crews involved in accidents do not fall under the same regulatory requirements as U.S. crews.
Hersman also said that two flight attendants in the rear of the aircraft were ejected after the impact and found on the side of the runway with injuries.
During a news briefing in Seoul on Tuesday, Asiana President Yoon Young-doo defended the pilots, saying they were "excellent" and qualified members of the flight crew with experience flying into San Francisco International.
Lee Kang-kook, who has almost 10,000 hours in the air, had previously flown into San Francisco 29 times as a co-pilot on Boeing 747s, Yoon said. Lee Jung-min, with almost 12,000 hours, had flown into the airport 33 times.
Yoon said he personally apologized to the families of the two Chinese girls who were killed in the crash. He said he planned to visit the crash site and meet with survivors and their families in San Francisco to apologize. He added that would assist the investigation in any way he could.
Weikel and Vartabedian reported from Los Angeles; Nelson reported from San Francisco. Times staff writers Victoria Kim and Kate Mather contributed to this report.