Inside Boeing’s factory lapses that led to the Alaska Air blowout

The near-catastrophic midair blowout of a door-sized fuselage panel on an Alaska Airlines 737 MAX 9 in January was caused by two distinct manufacturing errors by different crews on successive days last fall in Boeing’s assembly plant in Renton.

The first manufacturing lapse occurred within a four-hour window early Sept. 18. On the evening of the next day, in the space of about an hour, the second error was made by a different crew of mechanics, untrained to work on that fuselage panel, known as a door plug, according to federal investigative and internal Boeing records.

Boeing’s quality control system failed to catch the faulty work performed within those two windows.

The following detailed account of what happened as the MAX jet moved through the Renton factory — and of the characters now at the center of the investigation — is compiled from the transcripts of federal investigators’ interviews of a dozen Boeing workers, synchronized with an internal Boeing document obtained by The Seattle Times that tracked day-by-day the rework that led to the door plug lapses.