The need for Boeing to switch to another supplier for some interior work was also cited in the report released by the US Government Accountability Office (GAO) as a major risk to the schedule.
Air Force One – adorned with the American flag, the words “United States of America” and the seal of office – is known around the world as an Air Force White House.
The current aircraft has 4,000 square feet (372 square meters) of space on three levels, including a conference room and a medical suite.
The Boeing 747-8s are designed to be able to fly in the worst security scenarios, such as nuclear war, and are modified with military avionics, advanced communications and a self-defense system.
Boeing received a $3.9 billion contract in 2018 for two 747-8 jets to be delivered around 2024. The Pentagon said this year that the planes are unlikely to be delivered until 2026.
“Boeing is experiencing workforce limitations for aircraft mechanics due to a competitive labor market,” the GAO said in its report.
“They said an additional limitation is the lower-than-expected security clearance approval rate for the skilled workers needed to modify the planes.”
Boeing did not immediately respond to a request for comment.
In December 2016, Donald Trump, then President-elect of the United States, wrung from then-Boeing CEO Dennis Muilenburg a promise that the cost of replacing Air Force One would not exceed $4 billion.
Trump previously urged the government to cancel the purchase of Boeing’s new Air Force One, saying it was “ridiculous” and overpriced.