Boeing’s top executive is defending how the company handled communicating details about a new system on the 737 MAX as more operators acknowledge the new information they are learning is prompting them to update manuals and training.
“You may have seen media reports that we intentionally withheld information about airplane functionality from our customers. That is simply untrue,” Boeing President and CEO Dennis Muilenburg wrote to employees in an internal memo. “The relevant function is described in the [flight crew operations manual, or FCOM], and we routinely engage customers about how to operate our airplanes safely.”
Boeing has faced growing backlash since a pair of Multi-Operator Messages (MOM) issued earlier this month explaining that a feature on the MAX family called the Maneuvering Characteristics Augmentation System (MCAS) can automatically change pitch in manual flight mode. New to the MAX to help mitigate flight-control issues that the model’s heavier, larger engines and related design changes introduced, the system—one of several that can automatically adjust stabilizer trim—relies on certain parameters to determine when it is needed, and is meant to work in the background.
But Boeing recently learned that erroneous data from one sensor—such as an angle-of-attack (AOA) indicator—can cause MCAS to move the stabilizer and push the aircraft’s nose down when it is not needed. One of Boeing’s bulletins linked the issue to the investigation into the Oct. 29 crash of Lion Air Flight 610 (JT610), though it did not say MCAS played a role in the accident sequence.
JT610 took off early on the morning of Oct. 29 from Jakarta in good weather. The 737 MAX 8 crashed about 13 min. later, descending at high speed into the Java Sea. Preliminary analysis of the flight-recorder data suggests the crew struggled to control the aircraft, Indonesia National Transportation Safety Commission investigators said. The cockpit voice recorder has not been recovered.
The Boeing bulletins sent operators scrambling for more information on MCAS, and prompted several changes. An FAA directive issued Nov. 7 ordered MAX operators to update their flight manuals with Boeing’s MCAS information, though it does not require any new training or changes to the system itself. Three operators in Canada, working with Transport Canada, went further. They revised manuals, checklists and “supplemented” their training with MCAS information, WestJet said in a statement. Air Canada and Sunwing are Canada’s other two MAX-family operators.
U.S. operators have not announced changes beyond the manual updates, though several expressed concern over their lack of knowledge about MCAS.
“This is the first description you, as 737 pilots, have seen,” the Allied Pilots Association (APA) told American Airlines pilots, adding MCAS is not mentioned in the FCOM. Southwest Airlines issued a similar message to its pilots, and one operator’s MAX FCOM reviewed by Aviation Week did not mention MCAS, though it discusses stabilizer trim functions and emergency procedures.
The Air Line Pilots Association, writing to FAA and NTSB, expressed its concern over “a potential, significant aviation system safety deficiency” and asked the agencies for help in “clarifying the issues with respect to the pitch control system of the aircraft.”
The United Airlines Master Executive Council (MEC) has taken a different stance, telling the carrier’s pilots that while MCAS may be new, its function is not. As a result, pilots already knew how to manage a MCAS-linked problem.
“Despite the omission of the MCAS description in the initial 737 MAX differences training, United pilots are properly trained in handling an MCAS malfunction,” MEC safety committee chairman Bob Sisk wrote to members. “[W]hen working properly, the system helps us avoid stalls. If it faults or activates due to a related system fault (like an AOA sensor), it presents itself to pilots as runaway stabilizer trim ... something we can recover from using existing [checklist] procedures with the flip of the cutout switches.”
Investigators have said the three-month-old 737 MAX 8 that operated as JT610 experienced faulty sensor data on both the accident flight and several previous segments. Whether MCAS played a role in the JT610 accident remains to be seen, but the bigger-picture issue of how much pilots know about automated systems—and how well-prepared they are to manage failures—is emerging as a focus area.
A 2013 FAA-led study, “Operational Use Of Flight Path Management Systems,” highlighted the degradation of manual flying skills and difficulties transitioning from auto-flight to manual flight as serious, but often latent, safety risks. A rulemaking advisory committee suggested FAA develop training guidance for operators that addresses the issues.
“With regard to undesired flight states, it is always preferable to prevent occurrence,” the committee told FAA. “If prevention fails, early recognition of a developing undesired state with immediate correction is the second most preferred action. If both prevention and early recognition/correction fail, then recognition and recovery from the undesired state are required. A high level of competency in hand-flying (both the physical and cognitive aspects) is necessary for safe flight operations, regardless of the level of autoflight equipment installed, or used, in the aircraft.”
FAA is working on the guidance.