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Boeing failed to adequately test a flight control system on the 737 MAX that precipitated two crashes, the U.S. National Transportation Safety Board said in a report released Thursday that called on the U.S. Federal Aviation Administration to change how it assesses new aircraft to better account for how pilots respond in emergency situations.
In its testing, Boeing didn’t take into account how multiple warning indicators could confuse pilots, the report says. Before the 737 MAX returns to service, the NTSB wants FAA to require the plane maker to carry out a thorough assessment of pilot responses to the potential failure modes of the Maneuvering Characteristics Augmentation System (MCAS), as well as work over the longer term with industry and human factors experts to improve flight deck alerts and pilot training.
“They did not look at all the potential flight deck alerts and indications the pilots might face,” Dana Schulze, who heads the NTSB’s Office of Aviation Safety, said in a press briefing. “Multiple alerts and indications have been shown through years of research to have potentially an impact where pilots will not respond as perhaps you might have intended.”
The 737 MAX has been grounded worldwide in the wake of the crashes of Lion Air Flight 810 and Ethiopian Airlines Flight 302, which killed 346 people. In both crashes, malfunctioning angle of attack sensors are believed to have erroneously triggered the activation of MCAS, which was designed to push the nose of the plane down in conditions in which it might be in danger of an aerodynamic stall. Preliminary accident reports into both incidents have shown that the flight crews of both planes were subjected to a number of potentially confusing visual and auditory warning alerts and shaking of the captain’s control column. Boeing had assumed that pilots would quickly recognize any improper nose-down commands as a malfunction of the plane’s automatic trim system, which was present on the previous version of the 737, and use established procedures to deactivate the system and adjust the plane’s trim manually.
On Wednesday, Boeing’s board said that it wants the company to reexamine how it designs airplane cockpits and flight controls to meet the “needs of the changing demographics and future pilot populations”—a reference to concerns that the two crashes in Indonesia and Ethiopia have raised about pilot training standards in developing countries, where airlines have expanded service dramatically over the past few decades amid rising levels of wealth. The board also formed a new safety committee and sketched out organizational changes to strengthen the independence of Boeing’s engineers and safety certification representatives from commercial pressures.
The NTSB report makes seven recommendations to the FAA, including that it should develop diagnostic tools and methods to test its assumptions of how pilots respond to airplane failures and determine how aircraft makers could more clearly prioritize and present cockpit alerts to pilots.