Correction: This story, originally published May 11, 2016, listed an incorrect date for when the new aircraft will begin operations. The new Air Force One is expected to be up and running in 2024.

The Air Force on Tuesday gave Boeing the green light to start submitting design proposals for the new presidential aircraft that, by 2024, will shuttle a future president around the world.

The Air Force posted online an amendment to its Air Force One contract — also known as the Presidential Aircraft Recapitalization — authorizing Boeing to begin preliminary design activities.

In January 2015, the Air Force announced it had chosen the Boeing 747-8 as the platform for the next Air Force One, and gave the company a sole-source contract to modify the aircraft. If all goes well with the design and development process, the new presidential aircraft could be up and running in 2024. The aircraft are expected to last 30 years.

But the government has somewhat scaled back its plans for the new Air Force One. As recently as Jan. 29, the contract synopses on FedBizOpps said the government would buy "up to three" new aircraft. Now, the latest version of the contract synopsis said the government will buy two modified 747-8 aircraft from Boeing.

The 747-8 is the latest model of Boeing's 747. The Air Force said last year it determined a wide-body, four-engine passenger aircraft such as the 747-8 was necessary to serve as the next Air Force One.

In January, the Air Force also awarded Boeing a contract for conducting risk reduction activities for the new Air Force One — trying to find opportunities to cut costs and increase efficiencies while meeting the needs of fielding the new plane. Factors that drive the cost of the new presidential airplane include its maintenance, air refueling capability, and state-of-the-art communication equipment.

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This contract is only for the modification of the 747-8s. The Air Force is buying the airplanes under a separate contract.

The two airplanes now serving as Air Force One are Boeing 747-200Bs, with the tail codes 28000 and 29000. The first was delivered in 1990.

According to the White House's website, the iconic aircraft has onboard electronics designed to protect against an electromagnetic pulse and a secure communications system that would allow it to operate as a mobile command center in case of a nuclear or other serious attack on the United States.

The current Air Force One has 4,000 square feet of floor space on three levels. There is a suite for the president including an office and conference room, two galleys capable of producing 100 meals, quarters for Secret Service, senior advis ers and others who accompany the president, and a medical suite that can be used as an operating room. A doctor is always on board Air Force One.

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Stephen Losey covers personnel, promotions, and the Air Force Academy for Air Force Times. He can be reached at slosey@airforcetimes.com.