Northrop Grumman said Thursday that the US Air Force acknowledged making minor "computation" errors in weighing bids for a huge aerial tanker contract it won against Boeing.

The defense giant, part of a consortium with the parent of European aircraft maker Airbus, said the errors should have "no impact" on a review of the massive contract that is being protested by Boeing Co.

The 35-billion-dollar tanker contract was awarded in February to Northrop Grumman and its European partner, the European Aeronautic Defence and Space Company (EADS), parent of Boeing's archrival Airbus.

The Government Accountability Office (GAO), the investigative arm of the US Congress, is reviewing the contract. A decision is expected by June 19.

Five errors were discovered in the way the air force calculated a 25-year estimated cost for the aircraft, Northrop Grumman said in an email to AFP.

"During the protest review, the Air Force discovered five errors in the (cost) computation, which in turn caused a slight adjustment in the operating costs of the two aircraft," Northrop Grumman said.

Northrop said that "for all intents and purposes," the cost estimates of both aircraft remain the same and "the minor errors should have no impact on that ruling."

Because of other factors including system design and development, "Northrop Grumman's proposal was more advantageous to the government," the company said, quoting an Air Force statement.

On February 29, the US Air Force chose the team of Northrop and EADS to provide 179 aerial refueling tankers in a contract estimated at 35 billion dollars, one of the largest Pentagon contracts in recent years.

Boeing contested the decision with the GAO on March 11.

Mark McGraw, vice president and program manager, Boeing Tanker Programs, said in a statement at the time that Boeing's analysis of the data presented by the Air Force in support of its decision "shows that this competition was seriously flawed and resulted in the selection of the wrong airplane for the warfighter."