Boeing plans to webcast the event.
Spokeswoman Kate Bergman emailed journalists: "We have successfully completed a number of key lead-up milestones in recent weeks. We're on track for first flight in the coming days, as early as Tuesday, Sept. 17.
"Be advised that, as flight testing is dynamic by its very nature, the schedule for first flight is always subject to change due to weather conditions and other factors."
The new 787-9 is 20 feet longer than the original Dreamliner, the 787-8. The -9 will carry 250 to 290 passengers on routes of 8,000 to 8,500 nautical miles. That's about 40 more passengers and 300 nautical miles farther than the original 787-8.
The company hopes to deliver the first 787-9 to Air New Zealand in mid-2014 after six to nine months of flight tests.
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