The latest delay risks further upsetting President Donald Trump, who said he wants to fly in the new planes before the end of his term in January 2029.

The cost for Boeing’s current effort to build the two new jets is over $5 billion. The current Air Force One aeroplanes entered service in 1990.

The Air Force One program, which involves converting two 74 -8 aircraft into specialised jets equipped with advanced communications and defence systems to serve as the next generation of US presidential air transport, would be four years behind schedule with a 2028 delivery.

Boeing said in a statement that it is making progress on the program. “Our focus is on delivering two exceptional Air Force One aeroplanes for the country.“In 2018 received a $3.9 billion contract to build the two planes for use as Air Force One, though costs have since risen.

Boeing has posted $2.4 billion in charges against earnings from the project.

In May, the United States accepted a luxury Boeing 747 jetliner as a gift from Qatar. The White House asked the Air Force to rapidly upgrade the gift for use as Air Force One.

The government tapped defence contractor L3Harris Technologies to overhaul the 747 from Qatar.

Trump expressed his displeasure with Boeing over the delays earlier this year but ruled out European rival Airbus as an alternative.

Around the same time, Boeing CEO Kelly Ortberg said Elon Musk, who serves as an adviser to Trump, was “helping us a lot” in navigating the delivery of the presidential jet.

In June, Boeing hired a former Northrop Grumman executive, Steve Sullivan, to lead the Air Force One program, according to two people briefed on the matter.

Sullivan, who previously worked on key Northrop programs including the B-21 bomber, replaced Gregg Coffey, who moved to another role at the US planemaker.