The official U.S. Air Force production decision for the KC-46 aerial refueling tanker has been delayed because of a refueling boom loads issue.

Boeing said the problem was identified during flight testing of the Pegasus and that a Milestone C decision will now come in August instead of June.

Boeing's updated projection for initial KC-46 deliveries and the expected timing for delivery of the first 18 certified tanker aircraft -- a milestone known as Required Assets Available -- is now August of next year instead of March 2017, with the final delivery slated for January 2018, due "to ongoing complexities associated with qualification and certification of the aircraft's centerline drogue and wing-aerial refueling pod systems [WARP]."

More than 18 aircraft will be making their way along Boeing's factory line and in various stages of final change incorporation and certification by August 2017. The first 18 aircraft will be equipped with refueling boom and centerline drogue refueling capabilities as well as all other contract-required capabilities except WARPs.

The WARP systems required to complete full contractual RAA will be delivered separately in October 2018, the company said.

The KC-46 Pegasus, developed from the commercial 767 aircraft, will eventually replace KC-135 aircraft.