Flying Blind: The 737 MAX Tragedy and the Fall of Boeing

by Peter Robison

Back on the ground, the captain documented what had happened in the logbook, and Lion Air’s mechanics got to work clearing the plane for the next flight. The captain’s note included the alerts he’d seen—alt disagree, ias disagree, and feel diff press (indicating bad altitude, airspeed, and hydraulic pressure). He and the mechanics never saw the alert that would have pinpointed the problem—aoa disagree, suggesting a discrepancy between the left and right angle-of-attack vanes. The reason: Lion Air hadn’t paid for it. They had purchased a bare-bones MAX plane, with no such indicator. Moreover, Boeing had never disclosed the potential issue to customers. So the Lion Air maintenance team never knew to replace the bad vane. They turned off the power, followed the procedures for the other alerts, and, without any other reason to hold it back, the plane was allowed to depart the next morning. A quirk of the software, however, meant that after a power-down, the bad sensor would again feed into the captain’s controls on the left side. Suneja and Harvino would be unwitting guinea pigs, this time without a third pilot to guide them. The IOU that Boeing’s engineers had left dangling in the hastily completed software finally came due.