In October, Boeing CEO Dave Calhoun was asked how fast Boeing could raise output of its best-selling 737 Max after a spate of quality snags. He was upbeat: Boeing would get back to 38 jets a month and was "anxious to build from there as fast as we can."

As he sought to reassure investors about the recovery of Boeing¡¯s cash cow after another quarterly loss, one of the narrow-bodied jets was waiting at Boeing Field in Seattle for final tests and delivery to Alaska Airlines just six days later.

Four critical bolts were missing.