The most recognizable plane in the world is getting an upgrade, but it won't be ready for a few years.

While Air Force One is just a callsign for any Air Force carrying the US president, the term is often used to refer to the pair of iconic blue and white Boeing 747s with "United States of America" emblazoned on the side. From Hollywood to cable news, the current aircraft known as Air Force One have been made famous through frequent appearances when accompanying presidents on most of their trips.

The current modified Boeing 747s that fly the commander-in-chief – known in the Air Force as VC-25As – are on their way out after serving only five presidents for nearly three decades. It's time for the flying White House to enter the new jet age with a next-generation aircraft to fly the president, the Boeing 747-8i, in the same way passenger airlines are retiring their older Boeing 747s.

Designated as the VC-25B, the new jet is larger and more efficient than its predecessor. But bigger, in this case, doesn't necessarily mean better as the new Air Force One will actually be lacking some key features compared to its predecessor, despite the sky-high price tag.

Here's what we know about the highly-confidential program to replace the current Air Force One.

The entire program is costing over $5 billion

Despite a concerted effort on the part of the Air Force and President Donald Trump's administration, the total program is slated to cost $5.3 billion, according to DefenseOne. That price includes the aircraft purchase – around $800 million if purchased new, which they weren't – as well as the interior completion, special modifications, and a new hangar at Andrews Air Force Base in Maryland.

Trump had gotten the price of the program down from $4.4 billion to $3.9 billion, DefenseOne also reported, but that didn't include everything.

Boeing is keeping the exact cost of the jets a closely guarded secret, according to DefenseOne. The last program to replace the Air Force One aircraft, which began under President Ronald Reagan and was completed during the George H.W. Bush administration, only cost $660 million, the LA Times reported.

The two 747s were supposed to go to a bankrupt Russian airline

Boeing won't be building the new Air Force Ones from scratch and in fact, the Air Force will technically be buying the aircraft secondhand. As part of the cost-saving efforts, Boeing sold the government two 747-8i aircraft that were built and intended to be delivered to a now-defunct Russian airline, Transaero, a Boeing spokesperson confirmed to CNN.

"We got a really good deal," former Air Force Secretary Heather Wilson told Bloomberg in an interview.

The jets – which were selling for $390 million at the time of the deal, according to DefenseOne – were stored in California awaiting new owners. They were later flown to Lackland Air Force Base near San Antonio, Texas, according to The Drive.

Boeing presented four alternate options to save costs

The replacement program began under President Barack Obama but his successor would have the most say in the acquisition process. In 2016, a newly-elected Trump publicly complained about the high cost of the replacement program, which he stated was over $4 billion.

"Boeing is building a brand new 747 Air Force One for future presidents, but costs are out of control, more than $4 billion," Trump said in a 2016 tweet. "Cancel order!"

Then-Boeing CEO Dennis Muilenburg met with then-President-elect Trump at Mar-a-Largo in Palm Beach, Florida to discuss potential alternatives to lower the cost of the program with four options, according to DefenseOne. A $4.2 billion alternative was to purchase two new 747-8i jets but only install the presidential configuration on one and a standard VIP interior on the other while a $3.88 billion option involved only buying one new 747-8i and keeping one of the existing 747s.

Less expensive alternatives also included buying two new 747-8i aircraft but eliminating some of the Air Force's requirements or just installing VIP interiors instead of the presidential configuration demanded by the Air Force. All proposals were flatly rejected by the service branch, according to DefenseOne.

Expect a new paint job

Air Force One is the most recognizable plane in the world thanks to its stunning blue and white paint job but the new jets will be getting a makeover thanks to Trump, who first expressed his desire to repaint the planes in a 2018 CBS News interview. The new design features more red, white, and blue compared to the current model.

Trump kept a model of the jet with the new design in the Oval Office for visitors to see. It's unclear whether the other VIP Air Force jets painted in the timeless blue and white livery will be updated or if the plane's soon-to-be inaugural flyer, Joe Biden, will keep Trump's changes.

The owner's manual alone is costing $84 million

The Air Force announced in April that Boeing will develop the owner's manual for the new VC-25B aircraft and the service branch is paying $84 million for it, DefenseOne reported. The manual will reportedly contain over 100,000 pages and won't even be ready at the time of the jet's estimated delivery to the Air Force, with DefenseOne reporting that it will arrive in January 2025.

The $84 million is included in the $5.3 billion project cost.

The planes will last for around three decades

Like most aircraft, the new planes will only last between 20 to 30 years, according to DefenseOne. The current VC-25A aircraft are scheduled to be replaced just over three decades from their first flights with Bush in 1990 and 1991.

The timing is in line with when most Jumbo Jets will be retired from passenger airlines and cargo carriers around the world. Boeing has also announced an end date for the 747 program after over a half-century of flight, with Atlas Air scheduled to receive the last four models in 2022.

If the manufacturer stays the course and doesn't develop a new two-level, four-engine plane, the next flying White House may be a downgrade to a smaller jet like the Boeing 777X.

The new Air Force One can fly non-stop to nearly every populated continent from Washington but can't refuel in-air

The new VC-25Bs will have a range of 5,900 nautical miles, which is both less than some private jets from Gulfstream and Bombardier and the current Air Force One's range of unlimited miles. That's because the VC-25As have the capability of air-to-air refueling that allows them to fly for as long as the president desires while receiving top offs from airborne fuel tankers.

It's an impressive capability that can keep the president flying should there be no place to land, like in the event of war. But the feature has never been used, Air Force sources told DefenseOne, except in the Hollywood movie "Air Force One."

The 5,900-nautical mile range, however, should allow the president to fly non-stop from Washington to faraway locales like Tokyo, Riyadh, and Tel Aviv.

The Boeing 747s are bigger but more efficient

One of the staples of the Boeing 747-8i is its next-generation engines for General Electric that are more fuel-efficient than the aging engines on the current Air Force One aircraft. Flying the new aircraft will save the Air Force $1.9 billion, according to DefenseOne, despite the larger square footage that the 747-8i provides.

Despite the larger size, however, the VC-25Bs will have the same passenger capacity of 71 passengers, according to The Drive. That means more room for non-passenger spaces like the president's office, communications bay, medical suite, or private bedroom.

Trump will not be the first passenger

Trump flew his final flight on Air Force One on the morning of Inauguration Day from Andrews Air Force Base to his new residence in Palm Beach, Florida at his private club, Mar-a-Lago.

The jets are scheduled to enter service in 2024 and Biden will be the first commander-in-chief to fly aboard the new Air Force One. Trump may never step foot on it, despite all his input and efforts to keep costs down on the project, unless invited by Biden or a future president.

If Biden decides to run again in 2024 and is successful, he'll have a full four years to spend with the plane rather than a few months at the end of his term. But if he retires in 2025, his successors will have plenty of time to enjoy the new aircraft.