Boeing (BA) is delaying the maiden flight of one of its test 787 Dreamliner jets.

"Typical build and flight-test challenges" are holding back the sixth test jet's maiden flight, while workers are "finishing the structure and dealing with anything you have to deal with in getting a flight-test plane ready," Boeing spokeswoman Yvonne Leach told Bloomberg News .

Boeing has prioritized the other jets as the sixth is being used to certify its General Electric (GE) engines, Leach said.

The 787 has been plagued with delays and is now running almost three years behind schedule. Boeing aimed to have all six jets flying by June and certified for passengers as soon as October.

The 787 Dreamliner will be the first airliner built mostly out of composites, rather than aluminum.

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