In the wake of a highly critical report by the Government Accountability Office which concluded that the Air Force may have unfairly given the $35 billion contract for the new air-refueling tanker to a Northrop Grumman/EADS/Airbus consortium and its KC-45, the Defense Department has again opened bidding on the aircraft. The move, announced July 9 by Defense Secretary Robert M. Gates, gives Boeing another shot at retrieving the contract it lost. The new planes would replace the aging fleet of KC-135 tankers, now 47 years old and built on the frames of Boeing 707 airliners. Under the directive, Northrop Grumman was ordered to stop working on its tankers. The Defense Department will likely approve a new contract by year’s end.