Boeing's second KC-46A tanker/refueler has performed its first test flight, with test pilots conducting checks on engines, flight controls and environmental systems.

The test of the KC-46A for the U.S. Air Force took place earlier this week in Seattle, Wash.

"Adding a second tanker to the flight test program is very important as we move into the next phase of testing," said Col. John Newberry, U.S. Air Force KC-46 System program manager. "The team will initially use the aircraft to test mission system avionics and exterior lighting. Later, it will share the air refueling effort with the first KC-46."

Boeing said it is now conducting a post-flight inspection and will calibrate instrumentation prior to the next series of test flights.

Boeing was contracted in 2011 to design and develop the Air Force's next-generation tanker and is building four test aircraft. Two of them are configured as 767-2Cs aircraft and two as KC-46A tankers, which are based on the 767-2C.

The EMD-1, a 767-2C test aircraft, has so far performed more than 260 flight test hours, while EMD-2, the program's first KC-46A tanker, made its maiden flight last September and has now completed more than 180 flight test hours.

Boeing plans to build 179 KC-46 aircraft for the U.S. Air Force.