The U.S. Air Force has awarded a nearly $600 million contract modification to Boeing [BA] to conduct the initial design of a replacement for the Air Force One presidential jets, the service announced Sept. 13.

The 18-month contract modification calls for Boeing to incorporate a mission communication system, electrical power upgrades, a medical facility, an executive interior, a self-defense system, and autonomous ground operations capabilities into two commercial Boeing 747-8s, the Air Force said.

An artist's rendering of the future Air Force One. (Boeing photo)
An artist’s rendering of the future Air Force One. (Boeing photo)

A preliminary design review is targeted for the fall of 2018. The Air Force plans to award an engineering and manufacturing development contract modification to Boeing in the summer of 2018 to conduct detailed design, aircraft modifications, testing and delivery of two presidential aircraft.

“These aircraft will provide the president of the United States with safe, reliable and affordable air transportation equipped with all mission capabilities necessary to continuously execute the constitutional responsibilities of commander in chief, head of state and chief executive,” the Air Force said.

Aircraft modifications are expected to begin in 2019. The new jets are slated to be ready for presidential use in 2024.

In August, the Air Force awarded Boeing a contract modification for an undisclosed amount to buy the two four-engine, wide-body 747-8s. That modification followed awards to Boeing in 2016 for risk-reduction activity.

Through the Presidential Airlift Recapitalization (PAR) program, the Air Force aims to replace the two existing Air Force One aircraft, also known as VC-25As, which are modified 747-200s that have been in service since the early 1990s. In 2015, then-Air Force Secretary Deborah Lee James said the existing aircraft were experiencing growing problems with parts obsolescence, diminishing manufacturing sources and increased down times for maintenance.

The new aircraft’s cost has become almost as sensitive as the equipment that will be on board. Soon after being elected last year, President Donald Trump pressed Boeing to keep the price down. In its new announcement, the Air Force pledged to look for cost-saving opportunities during the program’s preliminary design phase.

“The Air Force is committed to working with Boeing to ensure the PAR program meets presidential airlift mission requirements, as well as the president’s affordability expectations,” the Air Force said.