Updated

Boeing Co. said Tuesday it has again delayed the first test flight of its long-awaited 787 jetliner, citing a need to reinforce part of the aircraft.

The inaugural test flight of the 787, a next-generation aircraft built for fuel efficiency with lightweight carbon composite parts, was originally planned for late 2007. But Boeing has postponed it repeatedly because of production problems and a strike that forced the company to close its commercial aircraft operations for eight weeks last fall.

Deliveries of the long-range widebody, meanwhile, already have been delayed four times. Customers had expected to get the first of the new jets in the first quarter of 2010 — nearly two years behind the original schedule. The delays have cost Boeing credibility and billions of dollars in anticipated expenses and penalties.

Boeing said it will not announce a new schedule for the first flight and deliveries for several weeks.

Shares of Boeing tumbled $3.12, or 6.7 percent, to $43.78 in morning trading.

The Chicago-based company said it identified a need to reinforce an area within the side-of-body section of the aircraft during recent tests on the first of the airplanes.

The 787 production team will continue testing the airplane, performing tests such as low-speed taxiing, Boeing said. Work also will continue on five other test planes and other 787s in the production system, it said.

The 787 is Boeing's first new aircraft since the 777, which was introduced more than a decade ago. The new plane is built for fuel efficiency with lightweight carbon composite parts.

Scott Carson, president and CEO of Boeing's commercial airplane division, said experts had identified potential solutions to the reinforcement problem, and that such modifications were not uncommon in the development of new airplanes.

"Consideration was given to a temporary solution that would allow us to fly as scheduled, but we ultimately concluded that the right thing was to develop, design, test and incorporate a permanent modification to the localized area requiring reinforcement," he said in a statement.

Boeing said its financial guidance will be updated to reflect any impact from the changes when the company issues its second quarter 2009 earnings report in July.

Paul Nisbet, an analyst at JSA Research, said the announcement was "not good news," and that Boeing had said in recent days at the Paris Air Show that the plane was ready to fly.

"I don't think it means much overall, but it certainly is a disappointment short-term," he said.