Structural block-point improvements progressively introduced to the -8 between Line Nos. 7 and 70 are paying dividends, particularly when it comes to the predicted empty weight of the -9, says Sinnett. “We have a very robust baseline and we've learned a lot of lessons. We're ecstatic with where we are with weight. When we hit firm configuration, we locked in on a number and we've just come down on that. As in any new aircraft design, at every turn there's a risk and an opportunity. On the -8, after firm configuration the weight grew, but the -9 is a more stable design that builds on the experience of the -8 in terms of structural static and fatigue.”

The 787-9 is 206 ft. long, or 20 ft. longer than the -8, with two five-frame stretch sections on either side of the wing. Although seating up to 290 passengers in a three-class layout, compared to 250 in the standard version, the -9 is designed to fly up to 8,500 nm, or 300 nm further than the -8. Maximum takeoff weight (MTOW) is just over 50,000 lb. more for the stretch and currently set at 553,000 lb. Boeing has managed to keep the weight target fixed since the firm configuration freeze in 2010, before which the MTOW was around 545,000 lb.

Another advantage the -9 development has over the -8 is that “people are more familiar with the material,” Sinnett adds. Additionally, the results of structural testing following the design improvements to the wing box and side-of-body have built confidence in the underlying capabilities of the composite primary structure. This has allowed Boeing to trim original design margins that Sinnett says now appear to have been somewhat “over-cautious.”

Sinnett also confirms that, contrary to widely published reports this summer, the hybrid laminar flow control (HLFC) system developed to reduce the empennage drag of the 787-9 has not been dropped. The feature, which is the first form of passive HLFC to enter commercial airline service, is “still on the baseline,” he says. Final assembly of the first 787-9 is expected to begin in Everett early in the first quarter of 2013, with first delivery to Air New Zealand slated for early 2014.