The U.S. Air Force said June 8 that it expects to receive its first KC-46A Pegasus tanker in late-spring 2018, months later than the December delivery that prime contractor Boeing [BA] has projected.

The Air Force, which recently completed its annual KC-46A “schedule risk assessment” with Boeing, attributed the delay to slow progress in flight testing and Federal Aviation Administration certification. Those factors had previously pushed back the projected delivery from September to December.

A KC-46 refuels an A-10 during testing. Photo: Air Force.
A KC-46 tanker refuels an A-10 during testing. Photo: Air Force.

“The Air Force will continue to support Boeing’s efforts to execute the program; however, the Air Force assessment predicts first aircraft delivery beyond Boeing’s forecast into late spring of 2018,” the service said in a statement.

Under its contract with Boeing, the Air Force considers the company responsible for any added cost caused by the delays. “These delays will not result in additional cost to the taxpayer,” the service said.

Boeing disagreed with the Air Force’s latest schedule estimate, saying it still expects to deliver the first KC-46A by December.

“While we do agree that there is risk (there is always some risk until testing in complete), we still forecast first KC-46 delivery by the end of the year,” Boeing said in a statement.

According to Boeing, the aircraft’s design has stabilized, the majority of development testing is complete, and a sixth aircraft has joined the flight-test effort, all factors that should help keep the program on track.

“The six aircraft have now completed approximately 1,700 flight-test hours to date,” the company said. “We are not discovering any new technical risk.”

The Air Force plans to buy 179 KC-46As to begin to replace its aging tankers. Boeing is expected to deliver the first 18 fully capable aircraft by October 2018, 14 months later than originally planned.