A mismanaged approach for landing in a highly automated cockpit was the probable cause of last July's crash of a South Korean airliner in San Francisco, US investigators said on Tuesday.
Three young Chinese citizens died and 182 people suffered injuries when Asiana Flight 214 from Seoul clipped a sea wall with its landing gear, then crashed and burst into flames, in the first commercial airliner disaster in the United States since 2009.
"In this investigation, we have learned that pilots must understand and command automation, and not become over-reliant on it," said acting chairman Christopher Hart of the National Transportation Safety Board (NTSB).
"The pilot must always be the boss," added Hart, a licensed pilot himself, at the end of a day-long NTSB hearing that concluded the federal agency's probe into the July 6, 2013 disaster.
While the Boeing 777 was in the hands of "a seasoned flight crew with a good safety record, they misunderstood the automated systems at their command," Hart said.
The NTSB, which never explicitly assigns blame, refrained from explicitly accusing the Asiana crew of pilot error.
Instead, it cited a long and varied list of contributing factors, from the Boeing 777's automated throttle system to pilot fatigue and jet lag after an otherwise routine 10-1/2 hour trans-Pacific hop.
Investigators testified that captain Lee Kang-Kuk, a seasoned Airbus A320 pilot transitioning to the bigger Boeing 777, cut the autopilot on final approach into San Francisco, where the instrument landing system was out of service on an otherwise clear sunny day.
Doing so put the auto-throttle on hold, meaning it would no longer automatically control airspeed, explained investigator-in-chief Bill English.
When the jet dipped below the correct glide path, Lee reacted by pulling the nose up - but the auto-throttle, still on hold, failed to deliver an expected burst of engine power that would have enabled the airliner to make the runway.
"The Boeing 777 is one of the more sophisticated and automated aircraft in service," Hart said.
"But the more complex automation becomes, the more challenging it is to ensure that pilots adequately understand it," he added.
English said Asiana, established in 1988 as a rival to Korean Air, emphasized "maximum use of automation" by its pilots, including the use of autopilots at as low as 1,000 feet (330 meters) from the ground.
Without mentioning Lee by name, English said the captain lacked sufficient practice in hand-flying the airplane, without the help of instrumentation.
"Pilot skills degrade if not practiced," he noted.
Lee flew into San Francisco with an instructor in the co-pilot's seat, Lee Jung-Min, who himself was freshly certified to train new 777 pilots. A first officer was in a jump seat.
While finding issues in the cockpit, the NTSB hailed the fact that 99 percent of the passengers and crew survived - and that 98 percent "self-evacuated" from the burning wreckage.
Flight attendants had performed "admirably and bravely," said Hart, who stressed the role that seat belts played in saving so many lives.
Of the three fatalities, one was hit by an exit door, while the others - hurled out of the aircraft on impact - had been seen by other passengers not buckling their seat belts for landing.
One of those passengers was later struck by a fire truck as she awaited help beneath the left wing.
For the flying public, Hart said, the lesson is clear: "Pay attention to your cabin crew's instructions. Make sure you are buckled in."
Asiana meanwhile said the NTSB "has properly recognised the multiple factors that contributed to the accident, including the complexities of the auto-throttle and autopilot systems, which the agency found were inadequately described by Boeing in its training and operational manuals."
"We again express our great sorrow for the accident, the loss of life and the injuries sustained by the passengers and crew."
"The NTSB made four training recommendations to Asiana, all of which Asiana has already implemented," the airline added in its statement.
In a statement, Boeing "respectfully" disagreed with the NTSB's suggestion that the complexity of its automated cockpits was a factor in the first fatal accident ever involving its 777 model, in service for two decades.
It said its auto-flight system had been used successfully for more than 200 million flight hours across several airplane models, and for more than 55 million safe landings.
"The evidence collected during this investigation demonstrates that all of the airplane's systems performed as designed," Boeing said.
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