"We look forward to working with the US Air Force on subsequent phases of the program allowing us to deliver the best plane for the president at the best value for the American taxpayer,"  Boeing spokesman Todd Blecher says in e-mail.

"We are currently under contract for $170 million to help determine the capabilities of this complex military aircraft that serves the unique requirements of the President of the United States," Blecher says

As a reminder, on Tuesday morning Trump called on Twitter for the cancellation of a Boeing contract to supply the Air Force One aircraft that has carried the American president around the world for decades, citing "out of control" costs. "Boeing is building a brand new 747 Air Force One for future presidents, but costs are out of control, more than $4 billion. Cancel order!" the president-elect tweeted on Tuesday.

Boeing is building two new versions of the 747 jumbo jet to replace the current fleet of aircraft, which have been in operation for more than three decades. Boeing declined to comment on the tweet. The contract is seen as vital to keeping open the production line of the 747, which first entered service in 1970.