Five years and two months after being selected to build the US Air Force’s new-generation KC-X aerial tanker, Boeing has launched its fourth and final test aircraft of the KC-46A programme.

The 767-2C aircraft, which will be used for type certification and is not currently outfitted for aerial refuelling, took off from the company’s widebody aircraft plant in Everett, Washington on 25 April and landed 1h and 40min later at Boeing Field, south of Seattle.

“During the flight, test pilots performed operational engine checks, flight controls, and environmental systems checks and took the 767-2C to a maximum altitude of 39,000ft prior to landing at Boeing Field,” says Boeing in a statement on 26 April. "[It] will be used to conduct environmental control system testing, including hot day/cold day testing and smoke penetration testing."

Boeing's second 767-2C-configured test aircraft (EMD-3) takes flight from Everett on 25 April

767-2C EMD3FirstFlight #1067 Tanker 466. Boeing Im


The aircraft, dubbed EMD-3, arrives as Boeing works feverishly to complete a “milestone C” review by the Office of the Secretary of Defence (OSD) that will unlock funding for the first low-rate production contract for seven aircraft, which Boeing has already begun building on its own dime.

The tanker manufacturer, which produced the US Air Forces' legacy 707-based KC-135 Stratotanker and inherited the DC-10-based KC-10 from McDonnell Douglas, is also working toward a KC-46A operational test and evaluation that is expected to start in May 2017 and must separately have 18 operational KC-46As in place by August 2017 to meet a contractual obligation known as "required assets available".

Boeing KC-46A refuels a US Navy F/A-18



This second 767-2C arrives as the "Pegasus" demonstrate aerial refuelling with the Lockheed Martin F-16 and Boeing F/A-18 and AV-8B warplanes for the first time. There’s no word yet from Boeing if it has rectified a possible software issue that has so far prevented boom refuelling of the large C-17 Globemaster III transport and the Fairchild Republic A-10 "Warthog". The tanker experienced "higher-than-expected boom axial loads" during in-flight contacct tests with the large, four-engine strategic transport in January and a fix is being investigated.

The far lighter F-16 fighter was successfully boom refuelled in January. Once the C-17 and A-10 boom refuellings are demonstrated, that completes the six required aerial tests needed prior to milestone C, and that includes receiving fuel from the legacy Boeing KC-10. A decision by Pentagon acquisition chief Frank Kendall to approve the KC-46A's entry into low-rate production was expected this month, and then in May, but now air force officials say June.

The first 767-2C test aircraft (EMD-1) first flew in December 2014 and has completed 315 flight test hours to date, says Boeing. The first KC-46 tanker (EMD-2) has logged about 240 flight test hours since its maiden voyage in September 2015 and the second tanker-configured aircraft, EMD-4, completed its maiden flight on 2 March.