Boeing engineers and test pilots considered before two fatal 737 MAX crashes whether an anti-stall system should be redesigned after discussing how flawed data from a single sensor could trigger it repeatedly, US investigators have found.
The so-called MCAS system, which relied on one sensor, has been linked in part to crashes of 737 MAX jets flown by Lion Air and Ethiopian Airlines, which triggered a worldwide grounding and a corporate crisis at the world’s largest planemaker.
The potential redesign discussed during 737 MAX development was ultimately ruled out, based in part on the assumption pilots would react in time to any malfunction, according to a National Transportation Safety Board report to Indonesian investigators.
Although not formally part of the required analysis, the Boeing staff discussed the scenario of repeated activation of MCAS due to erroneously high Angle-of-Attack data and considered whether a redesign was necessary, the NTSB report said, citing a 2019 presentation by Boeing to the agency.
“As part of this discussion they discussed the combined flight deck effects … but determined that no redesign was necessary,” the NTSB said of the Boeing discussion, referring to alerts that could be potentially distracting to pilots.
Later, in a review after the Lion Air 737 MAX crash last October which killed all 189 people on board, Boeing also found that presenting the scenario to regulators would not have led it to classify the anti-stall system as a bigger hazard at the time.
Boeing has redesigned the system to rely on more than one sensor and help reduce pilot workload as it strives to return the model to the air.
The fresh details of the design of the MCAS system from the NTSB are included in a final report by Indonesian officials into the Lion Air crash. The NTSB has been supporting the Indonesian-led probe.