Sixth Boeing 787 Dreamliner for flight test enters final assembly

The sixth and final Boeing 787 Dreamliner designated for flight test is now undergoing final assembly in Everett, Wash. The airplane, designated ZA006, will be powered with General Electric GEnx engines.

Boeing photo

Progress continues on the fleet. The first flight test airplane, ZA001, is getting its paint touched up this week before finishing factory testing. Power was brought onto the second airplane, ZA002, in late February and build verification tests are progressing well. Production work continues on ZA003, ZA004 and ZA005. In all, assemblies for 31 Dreamliners are currently in production throughout the supply chain.

Also observe the pre-painted doors in the aircraft. I wonder why? since the aircraft will in any case undergo a painting. Any answers ?