Only a few people at the FAA had even heard of it. “What’s MCAS?” asked one agency official. It was immediately clear that the software was far more powerful than Boeing had suggested in documents submitted to win the plane’s approval. The engineers had drastically underestimated the software’s ability to move the horizontal stabilizer, the small wing on the plane’s tail. What’s more, it had fired because of bad data from the single misaligned sensor—a flaw Boeing’s vaunted processes were supposed to find and root out long before the plane was in flight with commercial passengers.
