US President Donald Trump has informally struck a $3.9bn (£2.8bn) deal with Boeing for two new 747 jets for delivery by 2021.

The new aircraft will serve as an update to the ageing Air Force One 747 jets which have been in service since the senior Bush administration, reports Popular Mechanics. "President Trump has reached an informal deal with Boeing on a fixed price contract for the new Air Force One Programme," Deputy Press Secretary Hogan Gidley said on Tuesday. "Thanks to the president's negotiations, the contract will save the taxpayers more than $1.4bn."

In August last year, reports emerged saying that the US Air Force (USAF) was looking at purchasing two 747s that were originally built for a Russian airliner which went bankrupt in 2015. Each of the jets was reported to cost $386.8m. In the Pentagon's budget request to Congress last year, the USAF planned to spend about $3.2bn on the project in all. It is not clear if the new deal is an extension of this plan or if Boeing will build two new 747s from the ground up.

While the cost has now been updated to $3.9bn, Trump tweeted out in 2016 that the planes cost too much. "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 White House and Boeing are now saying that Trump did not have correct information at the time and that the actual estimate in December 2016 was more than $5bn.

One of the ways in which costs can be cut was proposed to Congress in September last year. It entailed removing the aircraft's aerial refuelling capability. No Air Force One till date has ever had to refuel mid-flight, and so the option seems redundant. Congress, however, was reportedly not pleased with the idea. The capacity to have a working Oval Office at all times, even if it means keeping the Air Force One for weeks in the air during national emergencies is considered too important to not have.

The transformation of a standard 747 to an Air Force One requires extensive work and three years is a really short time for Boeing to integrate enormous number modifications into the two aircraft. Air Force Ones typically have large meeting rooms, secure communications networks, electronics shielded against electromagnetic pulses, along with other defensive capabilities.