WASHINGTON — U.S. investigators are debating whether to blame a Boeing Co. jetliner’s design for helping cause a cascade of pilot mistakes in last year’s Asiana Airlines crash in San Francisco, which killed three teenagers.
The sticking point within the U.S. National Transportation Safety Board ahead of its final decision has been the extent to which the Boeing 777’s automatic throttle contributed to the plane’s loss of speed before it slammed into a seawall on July 6, 2013, said three people with knowledge of the discussions. They asked not to be identified because they weren’t authorized to speak.
The safety board on Tuesday is to decide on the probable cause and other factors leading to the crash, the first in the U.S. with passenger deaths in more than four years. While there’s little doubt the pilots made multiple mistakes, a finding that equipment on the 777-200 confused them could open Boeing to greater liability in lawsuits and shade public opinion.
“There’s quite a flurry of activity” in the days leading up to the NTSB’s findings in a major accident, said Peter Goelz, who served as managing director of the agency during the 1990s.
Such debate is consistent with prior investigations as the NTSB’s five-member board and staff hammer out nuances of what caused tragedies, Goelz said.
The NTSB has several options to address the role of the auto-throttle design. It can include it as part of the cause, list it as a “contributing factor,” or make recommendations for safety improvements that mention the equipment’s role.
The plane crashed after the Asiana pilots allowed it to get almost 40 mph slower than the target speed as they neared the runway.
Both Boeing and Asiana, which gave their recommended conclusions to the NTSB in March, laid primary responsibility for the accident on the pilots.
The Seoul-based airline and Chicago-based planemaker differ, though, over whether other issues were at play.
Boeing maintains the accident was solely the crew’s fault and would have been avoided if the pilots had aborted the landing, as required under airline procedures, said Miles Kotay, a spokesman, in an email.
“The airplane and all airplane systems were functioning as expected prior to impact and did not contribute to the accident,” Boeing said in its submission to the NTSB earlier this year.
Asiana urged the safety board in its March submission to find that the auto-throttle was a cause of the pilots’ mistakes. It also said the NTSB should recommend that the U.S. Federal Aviation Administration require Boeing to add a cockpit warning when speeds get too slow.
Groups with a stake in the outcome have met with the safety board’s politically appointed members in recent weeks in an attempt to influence the process, as is often the case before conclusions are announced on major accidents, said a person familiar with the proceedings.
The 777, like Boeing’s 737 and 787, has a suite of computer-driven tools in the cockpit to help reduce pilot workload. Such automation, which has also been adopted in similar ways by Airbus, is credited with helping reduce accidents and improve efficiency.
At the same time, pilot misunderstandings about automation have been studied for 20 years and linked to accidents, said David Woods, a systems engineering professor at The Ohio State University.
“This is an old story,” Woods said.
Recent accidents, such as the Feb. 25, 2009, crash of a Turkish Airlines Boeing 737-800 on approach to Amsterdam, which killed nine, have been linked to confusion over automation, he said. Woods called it the “creeping complexity” of the cockpit.
An FAA study released last year found that pilot reliance on cockpit automation systems has led to occasional confusion and new safety risks.
In the San Francisco accident, Captain Lee Kang Kuk, a veteran with Asiana who was being trained on the 777 wide-body, accidentally switched off the jetliner’s automatic speed control as he was trying to descend, according to NTSB documents.
The plane’s tail broke loose as it hit the seawall, and the fuselage then bounced and spun down the runway. The three girls who died may have been flung from the jet because they weren’t wearing seatbelts, according to statements to investigators by unidentified witnesses traveling with them.
More than 200 people were taken to hospitals. The plane held 291 passengers, 12 flight attendants and four pilots.
In almost all settings, the plane’s auto-throttle will prevent it from getting too slow, even if it’s switched off. Lee, 45, didn’t realize he’d put the jet into a rare mode that disabled this safety measure by making a series of changes to the auto pilot and throttles.
He “believed the auto-throttle should have come out of the idle position to prevent the airplane going below the minimum speed” for landing, the NTSB said in a summary of an interview with him. “That was the theory at least, as he understood it.”
Another Asiana captain, Lee Jung Min, 49, an instructor, was seated in the co-pilot’s seat.
Among the questions the NTSB also may decide are whether the pilots were adequately trained in the auto-throttle and whether Boeing’s documentation was sufficient to explain it.
The FAA required Boeing to add a note to the then-new 787’s documentation warning pilots they could lose speed protection under the same circumstances, according to NTSB documents. An FAA test pilot flying the 787 in 2010 said he was surprised to learn that the plane’s speed protection could be lost in some cases. The changes weren’t required for the 777.
The Asiana pilots neglected to notice a runway light system showing they were too low, didn’t monitor their speed and didn’t follow airline procedures to abort a landing if they weren’t properly lined up for touchdown, according to information released previously by the NTSB.
The 777, the world’s largest twin-engine jetliner, entered commercial service in 1995. Last year’s accident was the first involving fatalities and only the third serious enough to destroy a 777. A fourth 777 presumed destroyed is the missing Malaysian Air 777-200ER model, the same as the Asiana jet.
Boeing designed the auto-throttle to aid crews while not replacing them, John Cashman, the company’s chief pilot on the 777 program, told an NTSB board of inquiry on Dec. 11. The crew is “ultimately responsible for the safe conduct of the flight,” Cashman said.
Alan Levin: firstname.lastname@example.org.