The U.S. National Transportation Safety Board might be six months from declaring the probable cause and contributing factors in the Asiana Airlines 777-200ER crash in San Francisco last July, but two main participants in the investigation, Asiana and Boeing, have already formed their own conclusions. 

In documents submitted to the NTSB and published on March 31, both the airline and the manufacturer contend that a basic lack of monitoring and failure to follow airline and industry standards for abandoning an approach led the pilots into a situation where airspeed and altitude were too low to avoid crashing into the sea wall in front of Runway 28L, but the agreement stops there.

Asiana says its pilots were blindsided by lack of a timely low-speed aural alert and an autopilot flight-director system mode—flight-level change (FLCH)—that is inconsistent with practically all other modes in that it allows the autothrottle to go into a “hold” mode with engines at idle and no low-speed “wake-up” to prevent the aircraft from flying too slowly. Boeing, however, says the 777 and its automation systems and training materials were not at fault in the crash, but rather the pilots were not adept at visual approaches and did not take advantage of several opportunities to abandon the unstable arrival before it was too late. Asiana provides 11 recommendations in its submittal; Boeing offers none. 

It is unclear how any of the posturing could influence the NTSB’s determinations on the accident, or any of the more than two dozen civil lawsuits filed in the weeks after the crash, actions that blame both Asiana and Boeing for the accident. Given the potential liability in admitting to deficiencies while cases are ongoing, it is not surprising that Boeing is not offering recommendations on how to improve its aircraft, even if the company is internally contemplating changes to low-speed alerting systems or modifications to the autothrottle logic. Changes to the 737NG autothrottle and low-speed alerting systems, both of which played a role in the crash of a Turkish Airlines 737-800 crash in Amsterdam in February 2009, took more than three years to reach the fleet, either in the form of a service bulletin or an airworthiness directive. 

In the meantime, Boeing is staunchly defending the 777 FLCH mode, noting that aircraft equipped with the mode have performed 55.6 million successful landings, which it says equates to more than three landings per minute, every minute of every day for the past 32 years. FLCH is normally used for changing altitudes in cruise by selecting the mode and entering the target altitude on the mode control panel.

In the San Francisco crash, Boeing says the pilots “erroneously” pushed the FLCH mode button at 1,600 ft. while descending on autopilot toward the runway, causing the autopilot to climb toward a preset altitude of 3,000 ft. that had been set in case of a missed approach. The pilot-flying in the left seat, who was completing his transition training to become a 777 captain after flying the A320 as a captain for five years, turned off the autopilot and pulled the throttles to idle thrust to descend, an action that in FLCH mode puts the autothrottles in “hold.” On the flight deck, a green box in the flight-mode annunciator area of the primary flight displays would have highlighted the word “Hold” for 10 sec.; but no associated audible announcement would have cued the pilots to the mode change. In interviews, the pilots said they had assumed the autothrottle would have maintained the 137-kt. approach speed they had set in the mode control panel, despite their having had recent training in the nuances of FLCH. 

Regardless of the mode, Boeing says, the crew failed to monitor airspeed, thrust and altitude to verify a stable arrival. 

“At 500 ft., the approach was not in compliance with the industry-standard stabilized approach criteria for sink-rate and thrust settings,” states chief engineer for air safety investigation Michelle Bernson in the Boeing submission. “A go-around should have been initiated.” Below 500 ft., she states, there were “numerous clues”—visual and tactile—that showed the aircraft’s speed was decaying, the aircraft’s thrust setting was incorrect, and the aircraft was increasingly below glidepath. The aircraft ultimately slowed to 103 kt., well below its 137-kt. target speed before the pilots attempted a go-around. 

Thomas Haueter, a technical consultant for Asiana, says the automation design, combined with the high workload approach, may have been an accident in waiting. “You’re in a situation where the autothrottle does not wake up to the set airspeed and it does not wake up as you get near stall,” he says. Haueter, veteran NSTB investigator who retired in 2012, says none of the three pilots on the flight deck remembers pushing the FLCH button on the mode control panel, although Boeing notes the cockpit voice recorder captured “sound of click” at the same time the flight data recorder shows the FLCH mode activated, confirming “that the button was pushed.” 

Boeing questions the pilot-flying’s fitness for handling the 777, noting that in the most recent training flight before the accident, the instructor noted that he was not well organized and deviated “from multiple standard operating procedures.” During interviews after the accident, the Korean pilot-flying said, in English, that the approach into San Francisco was “very stressful” and that he was “very concerned” about his ability to perform a visual approach there.

Asiana doubts at least part of that assessment, noting that there was not a professional Korean translator in the room, the pilot sustained a broken rib that he had not yet been treated for, and his use of the word “stressful” in English was not as intended. Asiana had asked the NTSB to review the recordings of the interviews, but the NTSB says it did not retain a copy. “That’s not typical,” says Haueter. “Normally we kept absolutely everything until the [final] report was adopted.” 

Pilots on the morning of the crash were flying the “Quiet Bridge” visual approach that Asiana says kept the aircraft high and fast—compared to a normal instrument approach—until fairly close to the runway. Controllers instructed Flight 214 to maintain 180 kt. until 5 nm from the airport, more than 40-kt. above its planned final approach speed of 137 kt. 

In January, two crews of professional pilots gathered by the NTSB for a “simulator observational study” demonstrated that the Asiana pilots were not unique in getting behind the aircraft on the approach. The study used crews of pilots from Boeing and from the FAA. All “flew” a 777 simulator at Boeing in Seattle. Each crew performed 10 test flights, five of which simulated a “standard” approach profile; the balance followed the accident profile, including the altitude and speed restrictions that air traffic controllers issued to the accident crew. Asiana says the results indicate that both crews “had difficulty” achieving a stabilized approach by 500 ft. under the conditions matching the accident profile. “In fact, the aircraft was considered unstable due to excessive sink rates on four of the 10 test flights conducted under conditions matching the accident profile,” according to Asiana. 

The NTSB also evaluated go-around scenarios with the crews, determining that a “normal” go-around would have been possible 12 sec. before ground impact on the accident flight. Asiana notes that the 777’s “quadruple chime” low-airspeed caution sounded 11 sec. before impact on Flight 214, and the crew took an additional 3 sec. before advancing the throttles for a go-around. Boeing, however, says that the low-airspeed alert (the quadruple chime), which sounded 11 sec. before the crash, “provided a timely caution of decreasing airspeed.” Asiana is asking the FAA for a dedicated low-speed aural alert that will provide pilots with adequate time to perform a go-around. Boeing’s low-speed warning was originally developed for issues at altitude, and the chime is also used “with more than 70 other potential issues,” states the airline.

Asiana also uncovered some concerns about FLCH that were raised by the FAA in 2011. In a “response item” from 787 certification testing that Asiana obtained through the Freedom of Information Act, the  FAA had “strongly encouraged” Boeing to make changes to the 787 flight-management computer system to provide autothrottle “wake-up” capability to maintain a minimum flying speed in all autothrottle modes. Those modes are shared by the Boeing 777, 747 and 767.

The response item shows that an FAA pilot was performing certification stalls with artificial ice contours on the 787 in September 2010 when the concern first arose. “When in a descent such as FLCH with autothrottle in (hold) mode, and the descent has to be manually interrupted for something such as a traffic alert, the autothrottle will stay in (hold) mode and will not wake up [as] it does when you capture the original altitude,” the response item reads. “The speed will decrease well past maneuvering speed.” The FAA ultimately closed the item, but with the request for a software change to the flight-management computer at some future time.

The FAA discussed the origin of the response item during a December 2013 public hearing on the Asiana crash, but did not mention its request to Boeing to change the FLCH mode.

“Given [that it was not a safety or regulatory compliance issue], at that point, [the FAA pilot] believed it was an area where there still could be improvement and he worked with Boeing to include additional information in the flight manual to explain that the autothrottle on the 787 would not wake up from the autothrottle hold,” said Stephen Boyd, manager of the FAA’s airplane and flight crew interface branch, of the 2011 response item. 

Boeing’s former chief test pilot, John Cashman, called the issue a “misunderstanding” of when the autothrottle would wake up and when it would command speed. “In the end, when [the FAA pilot] understood that this design has 210 million flight hours, he felt it was not as critical of an issue,” said Cashman during the December 2013 hearing. 

Similar concerns had been voiced by the European Aviation Safety Agency (EASA) during its validation of the FAA certification for the 787. EASA noted that the lack of a wake-up function in FLCH represents an “inconsistency in the automation behavior” to the pilots. “Inconsistency in automation behavior has been in the past a strong contributor to aviation accidents,” the agency stated.

Boeing makes the case that an FLCH mode that tries to control speed in two ways—through the elevator, as designed, but also through the autothrottle, as requested—will represent an inconsistency in its design philosophy and could prove unstable. “To do this would violate [our] design philosophy—that the pilot is the final authority for the operation of the airplane,” states the manufacturer. “This philosophy has led Boeing to avoid designs in which the aircraft overrides the crew’s selected automation modes. There are some scenarios, such as when the aircraft is operating in a symmetric thrust condition due to engine problems, in which such a change could be potentially dangerous.”