Boeing has completed its 787-9 critical programme review, progressing through detailed design and on to design releases by engineering teams.
A key progression on the twinjet will see the US airframer expand its use of composite on the second member of the 787 family, as it looks to trim the aircraft's weight.
As part of its upgraded design - which includes significant structural changes in some areas of the aircraft - Boeing will transition the larger -9 to a wing featuring more composite, with carbonfibre-reinforced plastic (CFRP) in-spar ribs supplied by Korean Aerospace Industries.
Mark Jenks, 787 vice-president of engineering, said the first four inboard ribs of the 787-9's wing will be made from composite, rather than the current aluminium design.
However, he said the trade-off between the weight saving and the complexity of the engineering required does not justify rolling out the CFRP ribs beyond the first four. He added that the 787-8's wing in-spar ribs would remain aluminium.
Boeing has been undertaking an aggressive weight reduction programme on both the 787-8 and -9. A report by Hong Kong-based consultancy Aspire Aviation said the early 787-8s - Airplanes 7-19 - are 6.1 tonnes overweight, and Airplanes 20-33 in excess of 4 tonnes overweight.
Additional savings will come with blockpoint updates on Airplane 34 and 50.
The aircraft will return to its "original weight target with no overweight issue" by Airplane 90, said Aspire.
For the larger 787-9, Jenks said the curing mandrels for both of the stretched sections are complete, growing the aircraft's fuselage by 6.1m (20ft).
This is made up of two 3m stretches of the Kawasaki Heavy Industries Section 43 and the Alenia Aeronautica Section 46, respectively.
Jenks said Boeing has not yet made a decision on whether or not the 787-9's new horizontal stabiliser architecture - which includes an integral multi-spar box design - will be incorporated back into the -8.
The new empennage also includes a centreline-spliced horizontal stabiliser, similar to the design of the 777, rather than the two co-cured boxes joined with a central junction base design, as on the 787-8.
Boeing has an order backlog of 266 aircraft for the 787-9, with Air New Zealand as the launch customer.
Air New Zealand is the launch customer for the type