The US Air Force (USAF) is reportedly planning to seek penalties from Boeing for delay in the delivery of KC-46 Pegasus aerial refuelling and strategic military transport aircraft.

The delay comes on the heels of the USAF's announcement to move the formal production decision on the KC-46 tanker programme, also known as Milestone C, from June to August 2016.

The delay in delivery of the first 18 aircraft is due to complexities related to qualification and certification of the aircraft's centreline drogue and wing-aerial refuelling pod (WARP) systems.

The delivery has been delayed from March to August 2017, with plans to hand over the 18th aircraft in January 2018.

USAF spokesman Major Robert Leese was quoted by Reuters as saying: "The KC-46 contract does not contain pre-defined penalties for missing schedule deadlines.

"As with any contract schedule breach, the Air Force will seek consideration commensurate with the impact of the breach from Boeing."

"As with any contract schedule breach, the Air Force will seek consideration commensurate with the impact of the breach from Boeing."

Boeing has been contracted to deliver a total of 179 KC-46s to the USAF by 2028.

The first 18 aircraft will feature refuelling boom and centreline drogue refuelling capabilities and other contract required capabilities except WARPs.

Expected to be delivered separately in October 2018, the WARP systems will be required to comply with the full contractual required assets available.

Developed from Boeing 767-200ER, the KC-46 would replace the USAF's ageing KC-135 Stratotankers fleet.

Image: Boeing's KC-46A prototype in flight. Photo: courtesy of Ken Fielding.