Back in the 90′s, I spent a summer in Seattle working on a project with a former Boeing engineer, and I remember being astonished (and a little alarmed) when he told me about working on the 747 line. “That plane’s been in production for over twenty years, and there are still hundreds of parts that don’t fit together,” he told me, “The guys on the line know exactly where you have to re-drill a hole or just bang the thing together with a mallet.”  We were remodeling a house at the time, so I could sympathize, but with a key difference: houses don’t have to fly through the air with hundreds of passengers (and screaming babies) on board.