The US Air Force (USAF) has successfully completed the first flight of the second Boeing-built KC-46A Pegasus tanker (EMD-4) at Paine Field in Everett, Washington.
The new development comes after flights of the programme's first KC-46A tanker aircraft.
The latest flight saw Boeing test pilots conducting operational checks on engines, flight controls and environmental systems.
USAF KC-46 System programme manager colonel John Newberry said: "Adding a second tanker to the flight test programme is very important as we move into the next phase of testing.
"The team will initially use the aircraft to test mission system avionics and exterior lighting.
"Later, it will share the air refuelling effort with the first KC-46."
Prior to the next series of flights, the Boeing team will now conduct a post-flight inspection and calibrate instrumentation.
The aircraft is expected to conduct aerial refuelling flights with 18 USAF aircraft before the end of the year.
The USAF's KC-46A is a multirole tanker that can refuel all allied and coalition military aircraft compatible with international aerial refuelling procedures in addition to the transportation of passengers, cargo and patients.
Developed from Boeing's 767-200ER, the new range of aircraft is designed to replace the USAF's ageing fleet of KC-135 Stratotankers, which have served as its primary refuelling aircraft for more than 50 years.
Currently, the company is working on the contract to build 179 KC-46 aircraft for the USAF.
Image: Boeing's second KC-46 tanker (EMD-4) takes off from Paine Field in Everett on its first flight. Photo: courtesy of Gail Hanusa, Boeing.