The spar, the main structural component of the wing, is 82 feet 5 inches long. On the aircraft, it provides critical support for flight loads and the weight of the wings when the plane is not flying.
The KC-46A is based on the company's commercial 767-200ER airframe, and Boeing said workers at its 767 production line are gearing up for assembly of the next-generation tanker's aft and forward body structures, which will take place in November.
Installation of military-unique systems on the aircraft will begin in June and first flight for the fully provisioned tanker is scheduled for early 2015.
"The Air Force is really excited and pleased that our No. 1 modernization priority has begun fabrication and entered the factory at Everett," said Maj. Gen. John Thompson, U.S. Air Force Program Executive Officer for Tankers. "The Boeing team continues to make significant progress in the KC-46 development program."
The Air Force contract with Boeing calls for delivery of 17 KC-46A tankers by 2017. In all, the service will acquire 179 of the planes by 2027 if all contract options are exercised.