Airbus Military hopes to sign the final agreement with its seven Nato customers for A400M military transport aircraft by the end of 2010.
Airbus Military chief executive Domingo Urena-Raso told the Wall Street Journal at the Farnborough International Air Show that discussion among the seven governments on how to share the extra funding was taking longer than expected.
Apart from discussions between Airbus and Occar, the bilateral discussions taking place between the governments are slowing down the process, according to the Wall Street Journal.
In March 2010, the seven Nato governments reached a preliminary agreement after long negotiations to change the terms of the 2003 programme contract.
The delay and cost overrun in the €20bn ($25bn) programme has forced the governments to pay for an additional €3.5bn ($4.5bn) in funding.
The seven Nato nations are Belgium, France, Germany, Luxembourg, the UK, Spain and Turkey.