LONDON, July 19 (Reuters) - Boeing said on Sunday it remains on track to deliver two new Air Force One jets in 2028, but meeting that target will require additional spending on a program already years behind schedule and billions of dollars over budget.

Boeing was awarded a $3.9 billion contract in 2018 to build the aircraft, though costs have since ballooned to more than $5 billion. The aircraft are intended to replace the current Air Force One planes, which entered service in 1990.

"We're on track for 2028," Steve Parker, CEO of Defense, Space & Security, told reporters ahead of the Farnborough Airshow in the UK, adding that he expected the first aircraft to begin testing next year.

"I do expect to see some cost growth there as we come through and we finish off the wiring and the structures, as well as finishing up our own certifications."

In May 2025, the United States accepted a luxury Boeing 747 from Qatar for use as a temporary presidential aircraft. The jet has since entered service as a bridge aircraft. Security concerns led President Donald Trump to forgo flying the Qatari jet home from Turkey, opting instead to return aboard an older Air Force One.

The Air Force One program involves converting two Boeing 747-8 aircraft into highly specialized jets equipped with advanced communications and defensive systems. Even with a 2028 delivery, the program would be running four years behind schedule.