The US Air Force awarded Boeing a $600 million contract to begin preliminary design work to modify two 747-8s to replace the Air Force One fleet, the service announces on 13 September.

The contract modification includes incorporating the new presidential aircraft’s mission communication system, electrical power upgrades, a medical facility, executive interior, self-defense system, and autonomous ground operations capabilities onto two Boeing 747-8s.

The USAF will replace two 747-200-based VC-25As delivered in 1991 with two 747-8s originally built for Russian carrier Transaero, which filed for bankruptcy in 2015 before it could take delivery.

Though that move has been touted by the White House as a cost-saving measure, the USAF and Boeing will continue looking for ways to shed costs during the preliminary design phase.

"Following the award of the contract to purchase two commercial 747-8 aircraft, this contract award is the next major step forward toward ensuring an overall affordable program," says presidential airlift recapitalisation programme executive officer, Maj Gen Duke Richardson, in a statement this week.

The USAF expects to award the engineering, manufacturing and development contract by summer of 2018. The contract will lead the programme through aircraft modification, test and delivery.