Boeing Co said on Thursday it would delay first delivery of its 747-8 Freighter -- the biggest commercial jet Boeing has ever built -- to mid-2011 from the fourth quarter of 2010 to address issues discovered in flight tests.

The latest 747-8 Freighter delay, which many industry experts had expected, is the third announced by Boeing, the world's second-largest commercial plane manufacturer after EADS unit Airbus.   

The 747 delay is not expected to have an impact on Boeing's 2010 financial results. But it follows an August announcement by Boeing that it would push back first delivery of its long-delayed 787 Dreamliner until the first quarter of 2011.

That delay, combined with disruptions to Boeing's 747-8 schedule, have drawn criticism from customers.

"We recognise our customers are eager to add the 747-8 Freighter to their fleets, and we understand and regret any impact this schedule change may have on their plans to begin service with the airplane," said Pat Shanahan, vice president and general manager, Airplane Programs, at Boeing Commercial Airplanes, in a statement.

Boeing said it would add a fifth airplane to its flight test fleet to help ensure the company meets the new schedule.

Boeing took a $1 billion charge related to the 747-8 in the third quarter of 2009 because of high production costs and tough market conditions.   

The plane flew for the first time in February. Since then, Boeing has discovered issues, including a low-frequency vibration in certain flight conditions.

Boeing says the problems do not require structural changes to the airplane, but they have disrupted certification testing.

The 747-8 Freighter, about 18 feet (5.5 meters) longer than the 747-400, had been launched in November 2005 and was originally scheduled to start delivering in the fourth-quarter of 2009.      

Boeing has 76 orders for the freighter model of the 747 at list prices between $293 million and $308 million. Boeing gets paid by customers at delivery. - Reuters