Boeing Co's first fully equipped KC-46A refueling plane completed a four-hour inaugural flight on Friday, a milestone for the $49 billion program that has run into cost and schedule issues in recent years.
The company tweeted pictures of the aerial tanker it is designing and building for the US Air Force as it took off from Paine Field in Everett, Washington.
Boeing test pilots performed operational checks on engines, flight controls and environmental systems and took the tanker to a maximum altitude of 35,000 feet (10,668 m) before landing at Boeing Field, the company said in a statement.
"This first tanker flight is a key milestone for the program," said Air Force Colonel Christopher Coombs, who runs the program for the Air Force. He said the program would now run air stability tests, flight controls of the boom, and test the plane's aerial refueling pods.
Boeing said it would start aerial refueling flights with a number of U.S. Air Force aircraft before the end of the year, which would help pave the way for a decision in 2016 to move into low-rate production.