It will take so long to upgrade the new Air Force One’s defences that Donald Trump may never be able to fly in it as president, aviation experts believe.

On July 8, Mr Trump was forced to leave the Nato summit in Ankara in the old presidential jet – despite arriving in the new one – because of security concerns. He said it would take about a month to “max out” the aircraft and get its security systems up to standard.

However, aviation specialists are sceptical about that claim, saying upgrading the Boeing 747-8 would either take significantly longer or fail to address existing defensive flaws.

Richard Aboulafia, an aircraft industry analyst, said: “One month is inadequate to do anything of use. Maybe some paperwork?”

The president accepted the $400m (£300m) jet as a gift from Qatar last year, prompting criticism, even from allies. Mr Trump, who personally selected the plane’s red, white and blue livery, took his first flight on it on July 1.

The jet will spend a relatively short time as Air Force One, because it will be sent to Mr Trump’s presidential library when he leaves office. The next presidential election is due to be on Nov 7 2028.

Many experts were surprised at how little time it took to convert for presidential use. However, some suggested that the administration cut corners to prepare the jet in time for July 4, when it swept over Washington during celebrations for the 250th anniversary of American independence.

Karoline Leavitt, the White House press secretary, rejected these suggestions, saying: “The brand-new Air Force One is fully mission-ready and safe for Presidential travel today.

“This fall, it will undergo a short series of enhancements, taking approximately one month, to ensure it remains the most advanced, secure, and capable aircraft in the world. During this brief window, the President will fly aboard other aircraft in the Executive Airlift fleet.”

Nick Veronico, the author of Air Force One: The Aircraft of the Modern US Presidency, also cast doubt on claims the aircraft would take a month to upgrade.

The timeline “doesn’t seem realistic given the potential amount of work that will be required, coupled with… the problem of finding the skilled workforce”, he said.

Mr Veronico continued: “Retrofitting an aircraft with infrared countermeasures and laser defensive systems is not a trivial task and requires dozens of highly qualified mechanics and technicians.

“The wiring for these defensive systems has to be woven through the aircraft’s existing systems, inspected and tested before the plane is ready to return to flight.”

He predicted it would take a minimum of six months to “max out”, but added there was a “distinct possibility that [Mr Trump] will not fly on it as president”.

The precise security capabilities of the new Air Force One, a plane so opulent it is called a “palace in the sky”, have not been disclosed by the White House.

However, experts agree that fixing its defensive flaws will probably include installing anti-missile systems, such as infrared jammers that confuse heat-seeking rockets, alongside hardening the fuselage and other parts of the jet to protect against electromagnetic pulses.

Mr Veronico suggested “maxing out” the 250ft Boeing would cost anywhere between $40m (£30m) and $100m (£75m). However, Mr Aboulafia believed the cost of sweeping the aircraft for bugs and upgrading its defences could ultimately reach $1bn (£750m).

Mr Trump has refused to reveal how much it cost to retrofit the new Air Force One. Speaking to journalists before his first flight on the 747, he insisted it “cost very little, relative to what it would cost if we did it a different way”.

He then appeared to contradict himself, saying the US would not “build a plane like this, because we wouldn’t be willing to spend the kind of money necessary”.

When he departed the Nato summit in Ankara a week later, the president left on the old Air Force One at the request of the Secret Service, before swapping to the new model at RAF Mildenhall in Suffolk.

It came as the US ceasefire with Iran collapsed, and Israeli intelligence claimed to have uncovered a plot by the regime to assassinate Mr Trump. American officials questioned Israel’s claims, and the US secret service said the aircraft swap was made out of an abundance of caution.

The president, asked by reporters why he was travelling on the new jet if it lacked missile defence systems, said: “It has a lot of capability. But as I understand it, in about a month or so, they’re going to send it to have it maxed out.” He added: “It’ll take about a month.”