The US Air Force's (USAF) KC-46A Pegasus tanker has achieved Milestone C approval from the Office of the Under Secretary of Defense for Acquisition, Technology, and Logistics.
This certification from under secretary Frank Kendall will enable the USAF to proceed with the production of the Boeing-built multirole tanker.
The approval to begin low-rate initial production follows a series of aerial refuelling demonstrations such as refuelling an F-16 Fighting Falcon, C-17 Globemaster III and A-10 Thunderbolt II off the boom, and an AV-8 Harrier II and F/A-18 Hornet off both hose and drogue systems.
The KC-46 also demonstrated its receiver capability by taking fuel from a KC-10 Extender.
USAF Secretary Deborah Lee James said: "I commend the team for diligently working through some difficult technical challenges.
"The KC-46 programme has made significant strides in moving the Air Force toward the modernisation needed in our strategic tanker fleet."
The first two lots of low-rate initial production contracts will be awarded to Boeing within the next 30 days.
Boeing will supply a total of 19 aircraft and associated spare parts for a pre-negotiated $2.8bn combined value.
The first aircraft deliveries will be to McConnell Air Force Base (AFB), Kansas, and Altus AFB, Oklahoma, US.
A total of 18 tankers are expected to be delivered by early 2018.
The KC-46 still needs to complete schedule of Federal Aviation Administration and military certification flight testing that includes refuelling test flights, in order to achieve certification for aircraft in the Air Force and Department of Defense inventory.