A Boeing KC-46A tanker has refuelled another KC-46A for the first time.
The work took place during a four-hour flight in which the two aircraft refuelled each other, says Boeing in a statement.
The pair achieved the maximum offload rate of 1,200 gallons per minute, and transferred 38,100lbs of fuel. The activity involved personnel from both Boeing and the US Air Force.
"The milestone flight helps pave the way for the next phases of certification and specification compliance testing," says Boeing.
It adds that the KC-46 has completed 2,000 flight hours and 1,300 contacts with types including the Lockheed Martin F-16, as well as the AV-8B, A-10, C-17, and KC-10.
In late September, the USAF's Air Mobility Command revealed that boom scraping issues and a slew of completed test points could delay delivery of the 767-based type until 2018.