Boeing’s money pit of an Air Force One project just sank a little deeper.

The company said it’s making a substantial effort to get the first of two presidential planes out the door – four years later and for billions of dollars more than initially promised.

CEO Kelly Ortberg on Tuesday told employees via an internal email that the company is adding “significant resources” to deliver the heavily modified 747-8 jets by 2028. That ramp-up in production and certification resources in the Air Force One program cost Boeing an additional $280 million last quarter, the company announced in its quarterly financial statement.

The program’s cost overruns have now surpassed $3.1 billion. Boeing has agreed to foot that bill.

President Donald Trump has taken a particular interest in the new Air Force One planes. He persuaded former Boeing CEO Dave Calhoun in 2018 to sign a government contract that capped the cost to the American taxpayer at $3.9 billion. That contract has since been modified, growing the price tag to around $4.5 billion to include spare parts and other items.