The second boom being built will be installed on a test aircraft and three more will be produced. The first boom built is being used in laboratory tests.
"Our team is achieving significant milestones as we prepare for flight tests to begin, and we remain focused on delivering this capability on schedule," said Maureen Dougherty, KC-46 vice president and program manager. "The KC-46 boom is modeled after the proven KC-10 boom, which has performed extremely well in its 30 years of operation.
"We're enhancing its reliability, making it even better."
The KC-46A, based on the company's 767 commercial aircraft, is being built for the U.S. Air Force and will replace the aging KC-135. Boeing is contracted to deliver 18 aircraft by 2017 and a total of 179 by 2027.
The aircraft will feature a modernized fly-by-wire boom and hose and drogue systems for refueling any U.S. or allied fixed-wing aircraft. It will also be able to be refueled itself while in flight.