EVERETT — The Pentagon is expected to put its seal of approval on Boeing’s new KC-46 tanker later this month. That means the company can focus on ramping up production of the aerial refueling tanker as it races to deliver the first batch of 18 to the military. Boeing has already said it will not meet the August 2017 delivery deadline.

Developing the KC-46 Pegasus, which is based on Boeing’s 767 and assembled in Everett, has been a bumpy road, dogged by design and supply chain problems that have added up to more than $1.5 billion in cost overruns for Boeing. The next goal in the multi-role tanker’s development is approval from the Pentagon to officially begin production, a waypoint dubbed milestone C in the program’s timeline.

Despite the various delays and setbacks, “we believe that the aircraft has met all of the wickets that are required to meet milestone C, but of course that remains to be seen, so I’ll say stay tuned on that,” the Secretary of the Air Force Deborah Lee James said in a briefing Wednesday.

The latest problems arose during flight tests in the past few months. Refueling boom operators were unable to transfer fuel to the C-17 Globemaster III, a heavy cargo plane. As Boeing addressed the problem with the boom the military put off its decision on starting production.

Boeing made hardware and software changes that corrected the problem and successfully finished flight tests in July. The tests included passing fuel in flight to several U.S. warplanes, including the F/A-18 Hornet, AV-B Harrier, A-10 Warthog and even another KC-46.

Due to development delays, Boeing actually started producing KC-46s at a very low rate last year. Even so, company officials do not expect to deliver the first batch of 18 combat ready KC-46s until January 2018.

Boeing is streamlining its 767 assembly line as it plans to increase output of 767 freighters and KC-46 tankers next year to 2.5 airplanes a month.

When the tanker goes into service with the Air Force later this decade, some KC-46s could be based at Fairchild Air Force Base outside Spokane. The airfield is on a shortlist of potential locations.

Dan Catchpole: 425-339-3454; dcatchpole@heraldnet.com; Twitter: @dcatchpole.