The U.S. Air Force on August 18 awarded Boeing a $2.8 billion contract to begin low-rate initial production (LRIP) of the KC-46A aerial refueling tanker. Boeing will supply 19 of the modified 767-2C freighters over two production lots by August 2018, a year later than planned.

The contract award followed a Defense Acquisition Board review of the KC-46 program that resulted in a “Milestone C” approval on August 12 to progress to the LRIP phase. Prototype tankers were first required to complete a series of ground and airborne tests, which included refueling flights with F-16, F/A-18, AV-8B, KC-10, C-17 and A-10 aircraft as well as a cargo handling demonstration, Boeing said.

The four test aircraft—two configured as 767-2Cs and two as full KC-46As—had logged more than 1,000 flight hours as of the LRIP contract award.

“It’s an important day for the company and program,” said Leanne Caret, Boeing Defense, Space and Security president and CEO. “We’re excited about building low-rate initial production aircraft, and it’s possible only because of the hard work of the joint Boeing-Air Force team.”

Under the engineering and manufacturing development contract the Air Force awarded Boeing in 2011, the manufacturer was to deliver the first 18 production tankers by August 2017. The parties later revised the program schedule because of production, wiring and certification issues. Last month, they successfully tested a hardware fix to resolve a boom loading issue discovered during aerial refueling tests.

The Air Force expects completion of the first two LRIP lots by Aug. 24, 2018. Boeing plans to begin delivering production tankers to the service next year.