In the next step of a months long process, Boeing Co. (BA) won an Air Force contract to begin designing the next Air Force One presidential aircraft in a deal worth just under $600 million.

Current plans call for two new 747-8s planes to replace two aging VC-25A (747-200) presidential support planes.

The contract modification includes design plans for a mission communication system, electrical power upgrades, a full medical facility, an executive interior, a self-defense system and autonomous ground operations capabilities, the Air Force said in a statement.

The Air Force said it will work with Boeing to ensure the two new aircrafts meet the presidential airlift mission requirements and the President's "affordability expectations."

This is the second step in Boeing's deal to produce the next Air Force One. The first contract was for the purchase of the planes, this one is for design plans and a future contract expected next summer will work out details of manufacturing, test and delivery.

Boeing stock traded down 0.65% to $239.01 midday Wednesday.

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