Boeing on Monday firmly blamed the pilots for last year’s crash of an Asiana Airlines 777 in San Francisco, telling the National Transportation Safety Board (NTSB) that the crash “would have been avoided had the flight crew followed procedures.”
“This accident occurred due to the flight crew’s failure to monitor and control airspeed, thrust level and glide path,” Boeing said in a document submitted for the agency’s investigation of last July’s crash in which three passengers died.
Asiana partly agreed with Boeing in its own submission to the NTSB, but it also found fault with the design of the jet’s automated flight controls.
The South Korean carrier wrote that “the probable cause of this accident was the flight crew’s failure to monitor and maintain a minimum safe airspeed during a final approach.”
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However, its report cites factors it says contributed to the crash, including the logic built into the plane’s autothrottle software.
Boeing and Asiana agree that as the pilots came in to land, they expected the autothrottle to automatically supply engine thrust to maintain a minimum airspeed. In fact, in the flight mode they had engaged, the onus was on them to maintain the speed.
Asiana also faulted the cockpit alerting systems as providing “inadequate warning” that the speed had dropped dangerously low.
The discrepancy between the airline and the jet-maker pivots around Boeing’s flight-control design philosophy, cited in its submission as requiring “the pilot always has the final authority over any automation system.”
In an earlier NTSB hearing in December, Boeing staunchly defended this automation-control design.
The issue will now come under intense NTSB scrutiny as the agency does its final report on the July 6 crash.
Because the airport’s instrument-landing system was out of service that day due to construction, pilots had no digital glide path in the sky to follow. They had to manually land planes.
But Asiana Flight 214 from Seoul, with 307 people aboard, came in too low and, traveling at 120 mph, clipped the seawall short of the runway. The main landing gear and the tail of the big jet sheared off.
Six people were thrown from the back of the jet when the tail detached. Three of them died. These were passengers in a rear row of seats; none was wearing a seat belt.
The other three, who were seriously injured, were flight attendants strapped into their seats at the rear of the plane for the landing.
Meanwhile, the rest of the plane slid along the ground, bounced, spun 330 degrees and hit the ground again.
The passenger cabin remained largely intact, enabling the remaining passengers and crew to survive.
As the plane came to a stop, the right engine caught fire. Everyone was evacuated on slides before the fire spread to the passenger cabin and burned through the fuselage.
The twin accounts by Boeing and Asiana largely agree on the events leading up to that deadly conclusion.
While approaching the airport, at about 1,600 feet, the pilot apparently accidentally selected an automated mode called Flight Level Change, which directed the autopilot to climb to a higher level.
To correct this error and cancel the climb, the crew disconnected the autopilot and manually pulled the throttles back to idle.
Boeing’s design philosophy interpreted this action as a manual override of the autothrottle by the crew.
In other situations, for example cruising at 35,000 feet, the autothrottle will automatically come alive and increase thrust if the airspeed falls too low.
But at that moment on Flight 214, with the assumption that the pilot had taken control of thrust, the Boeing control logic transitioned the autothrottle to hold mode, meaning it was ready to adjust the thrust again only if commanded to do so by the pilot’s actions.
At this point, the autothrottle had ceded control to the pilots, but the crew had lost touch with what was happening.
With the engines at idle and the autothrottle on hold, the crew didn’t monitor the jet’s speed.
Doug Rice, a veteran commercial-airline pilot and a board member of the California Pilots Association, said foreign flight crews often lack manual flying experience.
He believes the Asiana pilots were unable to cope that day with the fact that the instrument-landing equipment was out.
“It wasn’t like it was dangerous,” Rice said. “It was a beautiful day. And they didn’t fly the airplane.
“They didn’t miss their touchdown target by a little bit,” he added. “They missed by a third of a mile.”
In the December NTSB hearing, John Cashman, the test pilot who flew the 777 maiden flight in 1994, defended Boeing’s flight-control logic.
“It goes back to that original philosophy: not changing modes in an autopilot that the pilot doesn’t command,” Cashman said.
He said the pilot has to have the authority, should he see oncoming traffic or some other reason to change course, to fully control the airplane.
Asiana mentions in its submission that this precise situation arose during a test flight of a 787 Dreamliner, which has the same flight-control logic.
In that instance, the Federal Aviation Administration (FAA) test pilot questioned the fact that the autothrottle didn’t wake up automatically when the speed dropped.
But an FAA manager at the December hearing testified that after discussions with Boeing “the FAA pilot determined that the fact that the autothrottle did not wake up was not a safety issue.”
Asiana recommends in its submission to the NTSB that Boeing insert more explicit warnings in its flight-crew training manuals about this specific circumstance and also that it should develop stronger alerting features to mitigate any automation “surprise.”
Rice said such steps, rather than changing the logic of Boeing’s flight-control philosophy, is the right response.
“I don’t believe the philosophy needs changed,” said Rice. “We need to make sure the pilots understand the philosophy and they must demonstrate that knowledge during their training.”
The San Francisco crash was the first fatal accident of a 777. The NTSB investigation continues and will eventually produce recommendations.
There appears to be no link to what happened with the missing Malaysian 777 lost in March.
Dominic Gates: (206) 464-2963 or firstname.lastname@example.org