The 787 is expected to make its first flight in 2009
Boeing has delayed again the launch of its 787 Dreamliner aircraft, blaming a strike by machinists and persistent production problems.
The 787's first test flight is now expected to take place in the second quarter of 2009, a few months later than planned.
Boeing still aims at delivering the first Dreamliner in 2010.
The aerospace giant expects its financial outlook for 2009 to be affected by the new delay.
"We will overcome this set of circumstances as we have others in the past, and we understand clearly what needs to be done to move forward," said Pat Shanahan, Boeing's general manager for the Dreamliner program.
It is the fourth major delay on the 787, which is now about two years behind schedule.
Boeing has struggled with late design changes and parts shortages for the carbon-composite aircraft.
A 58-day strike by machinists hit US-based Boeing factories in September and October.
The Dreamliner is Boeing's first completely new aircraft since 1995.
It takes advantage of new technology that allows much of it to be made of composites instead of aluminium, which means it is lighter and, Boeing claims, will consume 20% less fuel than other, similar-sized planes.
It also has a greater range than similar-sized planes, which Boeing hopes will mean it can open up new, direct long-haul routes.
Boeing has received over 800 orders for the Dreamliner so far. The first aircraft is to be delivered to Japanese carrier All Nippon Airways.