The dispute between the United States and European Union over subsidies for Airbus is so complicated that the World Trade Organization (WTO) will not be able to rule on it until next year, a WTO document shows.

The decision prolongs one of the most intractable transatlantic trade disputes, involving tens of billions of dollars, in which both the EU and United States claim the other is giving unfair support to its civil aircraft industry.

WTO dispute panels usually aim to give a ruling within six months, but the panel on Airbus subsidies was formed in 2005.

"It will not be possible for the Panel to complete its work within six months of the date of composition due to, inter alia, the substantive and procedural complexities of the volume of materials involved in this dispute," said a communication from the dispute panel chairman, circulated to members on October 20.

"The Panel expects to complete its work in 2009," it said.

In July the chairman of the dispute panel formed in 2006 to examine the EU's counter-claim against US support for Boeing also said his panel would not report until 2009.

There had been speculation the Airbus panel would issue a confidential preliminary ruling this summer, after it circulated a summary of the facts in the case to the parties in March.

Both sides could be found to have violated international trade rules, and Airbus has repeatedly called for negotiations to reach a long-term settlement.

But in April, Airbus CEO Tom Enders said he thought a negotiated settlement was unlikely.

Boeing outsold Airbus last year in the USD$80 billion civil aircraft market but its production has been hit by a seven-week old strike.

Earlier this month Airbus suspended plans to increase passenger jet production because of the global financial crisis.