Boeing is assembling a third KC-46A test aircraft for the U.S. Air Force's next-generation aerial refueling tanker program at the company's Everett factory, keeping the program on schedule to complete production of four test aircraft by the third quarter of 2014.

"In addition to the three KC-46A tankers now in production, our System Integration Labs are operational and we're assembling a second boom," said Maureen Dougherty, Boeing vice president and KC-46 Tanker program manager.

"We remain on track to deliver the initial 18 KC-46A tankers by 2017."

The KC-46A is based on the Boeing 767 commercial jetliner, a proven airframe in service as an airliner, freighter and tanker. Boeing has delivered more than 1,050 767s worldwide.

"Our teams are maintaining their focus on quality and productivity as we move the first tankers through production," said Scott Campbell, vice president and general manager of the 767 program.

The first test aircraft will roll out early next year. The first test flight of a fully provisioned KC-46A tanker is projected for early 2015, and the first delivery of a production aircraft to the Air Force is planned for early 2016.

Boeing expects to build 179 tankers by 2027 if all options under the contract are exercised.