The Boeing deputy who’d vetted the software design had categorized the risk of a failure as relatively minor. But the documents on file reflected the software’s earlier design (Revision C), not the more powerful version later added in flight tests (Revision E). They showed the stabilizer had the capacity to adjust a plane’s ascent or descent by only 0.6 degrees—in its final form, it had been given the authority to make adjustments at four times that angle. “When they changed the design it drastically changed the potential criticality of the MCAS feature,” one FAA specialist said. “And that was
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