A monthslong federal investigation into Boeing’s 737 Max plane has called into question some of the most fundamental assumptions used by manufacturers and regulators when certifying aircraft, and challenged Boeing’s repeated assertions that pilots should have been able to easily handle a malfunction on its jet.
The National Transportation Safety Board, which released the results of its review of potential lapses in the design and approval of the 737 Max on Thursday, faulted the company for making erroneous assumptions during the development of the jet and pushed for broader changes in the way airplanes are certified.
The agency said Boeing had underestimated the effect that a failure of new automated software in the aircraft could have on the environment in the cockpit. When activated, the system, known as MCAS, automatically moves the Max’s tail and pushes its nose down. The system contributed to two crashes in less than five months that killed 346 people and caused regulators around the world to ground the plane. Boeing did not fully inform pilots about how MCAS functioned until after the first accident.
The safety board calls for Boeing and federal regulators to revamp the way they assess the risk of key systems on airplanes, by giving more weight to how a cacophony of alerts could affect pilots’ responses to emergencies. The safety board’s suggestions are not binding, but the Federal Aviation Administration has accepted the vast majority of its recommendations in the past.
In conversations with airlines and aviation unions following the crashes, Boeing executives said that the accidents could have been avoided if pilots had simply run a standard emergency procedure. But officials with the safety board suggested that Boeing was too confident the average pilot could easily recover the plane in that situation, because the company had not considered the chaos that ensued inside the cockpit.
Dennis Tajer, the spokesman for the American Airlines pilots union, agreed with the investigators.
“They completely discounted the human factor component, the startle effect, the tsunami of alerts in a system that we had no knowledge of that was powerful, relentless and terrifying in the end,” Mr. Tajer said of Boeing.
Boeing continues to grapple with fallout from the two fatal crashes. The Max remains grounded, as the company and federal regulators face multiple federal investigations into how the plane was built and certified in the first place. In a meeting last month, Boeing struggled to answer a raft of questions from international regulators and the F.A.A. about a software fix it has been working on to make the plane safer.
Two investigators handled the bulk of the work for the N.T.S.B., reviewing thousands of pages of documents, interviewing officials at Boeing and the F.A.A. and studying black-box data from the two crashes, in Indonesia and Ethiopia. They focused on MCAS, which sent both planes into nose dives.
When Boeing developed the Max, it assumed that if MCAS activated erroneously, pilots would immediately react by performing a standard emergency procedure. But the company had tested the possibility of an MCAS failure only in isolation, failing to account for just how chaotic the cockpit would become when the activation caused other malfunctions.