Washington: Boeing said on Monday it would formally challenge a decision by the US Air Force to award a $35 billion aerial tanker programme to a team led by Northrop Grumman and Europe's EADS.

"This is an extraordinary step rarely taken by our company, and one we take very seriously," Jim McNerney, Boeing chairman, president and chief executive officer, said in a statement.

Boeing said it would ask the Government Accountability Office, the investigative arm of Congress, to review the February 29 decision that has triggered outrage from some lawmakers sympathetic to Boeing and unhappy the winning bid features EADS' Airbus aircraft. Airbus is Boeing's chief rival in the commercial sector.

Boeing said on Friday it had "significant concerns" about the decision following an Air Force briefing on why it lost the contract award. The company said it conducted a "rigorous analysis" of the Air Force evaluation.

McNerney said based on "what we have seen," Boeing continues to believe it had the "most capable, lowest risk" and most cost-competitive bid over the life of the programme.

"We look forward to the GAO's review of the decision," he said.

Northrop completed its debriefing on Monday, and said the Air Force called its winning bid "more advantageous to the government" in the key areas of capability, past performance, cost and refuelling performance.

Air Force officials said last week that the Northrop-EADS bid was superior in a number of areas.

Northrop said in a statement the Air Force review was "the most rigorous, fair and transparent acquisition process" in Pentagon history. "Until we have had the opportunity to review the specifics of the protest, we will not comment further," Northrop said.

Lt. Col. Michael Paoli, a spokesman for the Air Force, said: "We still have great confidence in the openness and transparency of the KC-45A acquisition process."

Democratic US Senator Patty Murray of Washington state called the Air Force decision "short-sighted" based on economic and national security concerns. "It is my hope that the GAO moves forward with its review in a thorough matter," Murray said.

Contract: EADS sees no dispute

European aerospace group EADS defended a controversial contract to provide aerial refuelling tankers to the US Air Force yesterday after defeated rival Boeing announced an appeal.

"We have the feeling that the process was very transparent and fair and professional," chief executive Louis Gallois told a news conference. "It is not by chance that we won, having won the last five [international] competitions for tankers; that is all I can say," Gallois said.