The US Air Force has announced a further delay to awarding the $2.5bn maintenance contract for its air-to-air refuelling tanker aircraft, the KC-10.

The competitors for the periodic maintenance of the aircraft, Boeing and Northrop Grumman, expected the formal declaration of the contract by June or July 2009 but the decision has now been put back to the 30th September.

The award was delayed on the grounds of insufficient cost and pricing data submitted by all the contractors, reports Reuters quoting the US Air Force spokeswoman Lieutenant Colonel Linda Pepin.

Following as an effect, the Pentagon’s Defense Contract Audit Agency recommended a full audit of all vendors.

The contract was supposed to be awarded in June 2008, following bids received by the US Air Force from all the companies in late 2007.

Boeing was awarded the maintenance extension contract in January 2008 and the company will exercise the four-month options until January 2010, the end of the contract.

Additionally, Northrop Grumman has submitted a best-value proposal and is looking forward to winning the contract.