Boeing and regulators had approved the design under the assumption that flight crews could recognize and override a malfunction of the system within a few seconds. Even though the system could have been disabled by flipping two cockpit switches, pilots on a Lion Air flight departing from Jakarta on Oct. 29, 2018, and an Ethiopian Airlines plane leaving Addis Ababa on March 10, 2019, became confused, lost control and crashed.
The feature, known as Maneuvering Characteristics Augmentation System, was designed to make the Max feel exactly the same to pilots as the earlier family of 737s known as the Next Generation. However, the system was triggered erroneously by a single sensor that failed in both crashes and it continued to push the nose down repeatedly.