The US Defence Department on Wednesday formally reopened bidding for the contract to build the next generation of Air Force tanker refuellers, according to dpa. The contract was initially won by the Northrop Grumman-EADS partnership but a congressional oversight agency upheld a protest by rival Boeing, effectively forcing the Pentagon to rehold the competition for the 35-billion-dollar contract. The Pentagon on Wednesday formally asked the companies to resubmit proposals to build the 179 KC-X aerial refuellers. A final request will take place in mid-August and the companies will be asked to submit their proposals by October 1. The Government Accountability Office (GAO), an investigative arm of Congress, ruled in a June 18 report that the Air Force made critical errors in awarding the contract to Northrop and the European Aeronautic Defence and Space Company. The GAO concluded the Air Force overlooked key aspects of the Boeing proposal that could have tilted the competition to the American aerospace giant's advantage and urged the Pentagon to reopen the bidding. Shay Assad, the Pentagon director for acquisition, told reporters that the new request was a modification of the previous one that includes GAO's recommendations. Among them was to give greater consideration to the cost of operating the aircraft over 40 years. "Most of what's there really addresses the GAO finding and that exactly what we are trying to do," Assad said. There will also be greater attention to how much fuel the planes can carry, he said. Boeing has offered to use its 767 for the aircraft, while Northrop/EADS is using the larger A330. Defence Secretary Robert Gates announced July 9 that he had accepted GAO's findings and planned to restage the competition in an expedited process, citing the need to quickly replace the Air Force's aging fleet of tankers.