Boeing has pushed some factory work on the 787 Dreamliner to the uncovered tarmac outside its assembly plant in Washington state in an effort to keep churning out the popular plane at a rate of one every three days, according to people with knowledge of the situation. The unusual shifts, details of which have not been previously reported, are partly a response to unfinished jobs building up as 787s move along the assembly line and partly an effort by Boeing to speed up the factories.