Asiana Flight 214's pilots caused the crash last year of their airliner carrying 307 people by bungling a landing approach in San Francisco, including inadvertently deactivating the plane's key control for airspeed, the National Transportation Safety Board reported Tuesday.
But the board also said the complexity of the Boeing 777's autothrottle and auto flight director — two of the plane's key systems — contributed to the accident.
The 777 has been in service 18 years and is one of the world's most popular wide-bodied airliners. Until last year's accident, it had not been involved in a single fatal crash.
The board's acting chairman, Chris Hart, warned that the accident underscores a problem that has long troubled aviation regulators — that increasingly complicated automated aircraft controls designed to improve safety are also creating new opportunities for error.
The Asiana flight crew "over-relied on automated systems that they did not fully understand," Hart said. "In their efforts to compensate for the unreliability of human performance, the designers of automated control systems have unwittingly created opportunities for new error types that can be even more serious than those they were seeking to avoid."
The South Korean airline's pilot training also was faulted.
Three of the 307 people on board Flight 214 were killed in the July 6, 2013 crash. Forty-nine people were seriously injured.
Asiana Airlines said it has already implemented the NTSB's training recommendations.
Boeing immediately rejected the notion that the 777's automated systems contributed to the accident. "The auto-flight system has been used successfully for over 200 million flight hours across several airplane models," the company said.
The board, which made 27 recommendations to prevent future disasters, didn't say that the autothrottle failed to perform as designed. But rather that its design could lead to confusion as to whether it was controlling speed or in an inactive state.
Investigators said the flight's three veteran pilots made several errors during the landing approach. They unknowingly disabled the auto-throttle, which they thought would keep them from flying too slowly, and failed to follow airline procedures in the sequence of instructions and in saying aloud what they were doing.
The plane was too low and too slow as it neared the runway. Its tail struck a seawall and was ripped off. The rest of plane went spinning and sliding down the runway.
The safety board also reported that two of the three people who were killed weren't wearing their seatbelts and were thrown from the plane.
Contributing: New York Times