The Dreamliner project was already behind schedule
Boeing has announced that it will delay the maiden flight of its new Dreamliner 787 aircraft, the latest postponement to hit the project.
The flight had been due to take place on 30 June, but the firm said it had now been delayed because of a need to reinforce a side section of the plane.
First deliveries will be put back further because of the delays.
Last week, Boeing told the BBC that the Dreamliner would make its first flight "in a couple of weeks".
'No materials problem'
Boeing denied that the latest delay to befall the Dreamliner was due to the plane being constructed from a large proportion of plastic composites instead of aluminium to keep down its weight.
"Structural modifications like these are not uncommon in the development of new airplanes, and this is not an issue related to our choice of materials or the assembly and installation work of our team," said Scott Carson, chief executive of Boeing Commercial Airplanes.
He added that while difficult, the fresh delay was the "prudent" decision.
"We are already working towards a solution and are focused on continuing our progress," said Mr Carson.
Tour of the Dreamliner: first broadcast July 2007
Scott Fancher, vice president of Boeing Commercial Airplanes, added: "We are talking about a one or two square inch area along the upper wing joint. It is a very limited area that needs structural reinforcement."
Boeing said it would not now be releasing new dates for the first flight and deliveries for several weeks.
Before the latest announcement, the long-range, medium-sized Dreamliner was already more than two years behind schedule.
Aviation analyst Jack Ablin of Harris Private Bank in Chicago said Tuesday's news "seems like a big setback".
"I'm hopeful that this issue can be resolved quickly. But my sense is that if it's big enough to delay the introduction then this is a serious concern."
Shares in the firm fell 6.5% in New York, closing at $43.87.
Boeing has received 865 orders for the Dreamliner, which makes it the plane-maker's fastest selling model.
The Dreamliner is the company's first completely new aircraft since 1995.
Boeing says the use of plastic composites means it will consume 20% less fuel than similar-sized planes.
It also has a greater range than other planes of its size, which Boeing hopes will mean it can open up new, direct long-haul routes.
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