Investigators of the Asiana Airlines accident that took place last July at the San Francisco airport have recommended Boeing to modify flight controls of its 777 jetliner to make them more user-friendly.
Although the 11 month investigation by the National Transportation Safety Board (NTSB) into the accident that killed three people and injured 180 didn’t find any technical faults or failures, the investigators believe making the system which automatically controls air speed in the 777 more intuitive, would prevent possible future incidents.
The review found the pilots committed 20 to 30 errors in the final 14 miles of the approach and didn’t understand properly the auto throttle function. Mismanagement by the pilots, who were said to be experienced, was identified as the main reason behind the accident.
"The automation performed as designed, but the pilots did not fully understand what the automation would and would not do," NTSB Acting Chairman Christopher Hart said. "It was not a design issue by itself, it was the intersection between the design and the pilots' understanding of how the design worked."
An auto throttle allows a pilot to control the power setting of an aircraft's engines by specifying a desired flight characteristic, rather than manually controlling fuel flow.
The 777 auto throttle protects against low speed, and will even wake up from being off to correct speed. But in "hold" mode, the system requires a pilot to control speed, and will not prevent speed from slipping below the minimum needed to stay aloft, the NTSB said. The Asiana flight's system was in "hold" mode and the pilots did not realize the risk, the NTSB said.
Had "wake up" been designed to occur in "hold mode," the auto throttle "would likely have increased 20 seconds before impact, which may have prevented the accident," said Roger Cox, a senior NTSB air safety investigator.
The board recommended that Boeing develop and evaluate changes to the control systems to ensure the plane's "energy state" - a combination of speed, altitude, engine thrust and other factors - "remains at or above the minimum desired ... for any portion of the flight."
Boeing said it "respectfully disagrees" with the NTSB's finding that the automated system on the 777 contributed to the accident. "We do not believe (it) is supported by the evidence," spokesman Doug Alder said in a statement. "We note that the 777 has an extraordinary record of safety - a record established over decades of safe operations."
The Boeing 777, a wide-body, long-range aircraft, had no prior fatal accidents since its introduction in 1995.
The 777 auto-flight system has flown more than 200 million hours on several models and made more than 55 million safe landings, Boeing said.
The company will, however, review the board's recommendations carefully but said any potential changes to systems must be weighed "with due consideration for the potential unintended consequences."
Overall 30 findings have been made during the NTSB investigation with recommendations addressing the Federal Aviation Administration, Asiana Airlines, Boeing, firefighters and San Francisco city and county.
Insufficient training on the side of Asiana Airlines and too complex flight training manuals have been named among the culprits of the accident.
The NTSB said the airlines may not have properly trained the co-pilot who was supervising the captain during his first landing at the San Francisco airport in a Boeing 777.
Asiana said the NTSB had "properly recognized 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. The recommendations made by the agency can help ensure such an incident does not happen again."
The airline also said it had already implemented the four training recommendations the NTSB made for its own operations and had further strengthened training and safety.