US Air Force officials and Boeing engineers have started the yearslong process of replacing Air Force One, the legendary aircraft that whisks the president of the United States and his entourage around the world.

The Pentagon last week approved the first of a series of contracts with Boeing, the US aerospace giant chosen to convert a pair of its 747-8 jumbo jets - there are actually two Air Force Ones - into state-of-the-art, luxury command centers.

That first contract, worth a relatively small $25.7 million, is for Boeing to look for cost savings and get a better sense of the scope of the massive task at hand, the Air Force said.