Boeing's share price plunged almost 9 per cent after the plane maker postponed the test flight of its first new aircraft in more than 10 years.

The company said that problems with the body of the revolutionary 787 Dreamliner had forced it to delay the test, scheduled for the second quarter of 2009.

It will be several weeks before Boeing will be in a position to give a new test flight date or details on how far the delay will push back delivery of Dreamliners, which is Boeing's first new plane since the 777 was developed more than a decade ago.

It is the fifth time the flight has been postponed, damaging Boeing's credibility at a time when the company is already struggling with cancelled orders due to the economic downturn.

Boeing's shares were down 7.61 per cent at $43.33, having dropped almost 9 per cent in morning trading.

The company will update investors on the financial impact of the delay when it announces its second-quarter figures next month.

Scott Carson, president and chief executive of Boeing Commercial Airplanes, explained that ground testing had shown that the side of the body of the aircraft needed to be reinforced.

"Structural modifications like these are not uncommon in the development of new airplanes," he said. "This is not an issue related to our choice of materials or the assembly and installation work of our team."

The Dreamliner is the first aircraft to be made mainly of carbon fibre rather than aluminium, making it lighter and more fuel-efficient. The advance has been keenly awaited by airlines that have struggled with the soaring price of oil in recent years.

The aircraft was originally scheduled to make its first flight in the summer of 2007, with delivery to airlines by early 2008, but the test has been delayed four times previous due as industrial action and production problems have delayed the Dreamliner's development.

With the economic downturn hitting business in the travel industry, airlines have cancelled their orders for 45 Dreamliners, although Boeing said earlier this month that it had orders for more than 850 of the planes.

A spokesman for All Nippon Airways of Japan, the first customer due to receive the Dreamliner, described the postponed test flight as "disappointing". "We will urge Boeing to clarify the entire schedule regarding 787 as soon as possible," he said.

Craig Fraser, an aerospace analyst at Fitch Ratings, said that it was unclear how badly the delay would impact Boeing's financial performance.

"If this is just a temporary delay of a few weeks, it's probably not much of an issue for the program or financially," Mr Fraser said. "If it turns out to be a modification of the airplane that takes several months, it could be costly."

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