Editor's note: This story was originally published at 2:07 p.m. EDT May 27, 2016.

WASHINGTON – Boeing's KC-46 tanker program will miss a major contractual deadline to deliver 18 ready-to-go aircraft to the US Air Force next year.

Due to ongoing issues with the KC-46's refueling systems, Boeing will not be able to deliver the 18 certified tankers to the Air Force as planned by August 2017, a major contractual obligation known as Required Assets Available, or RAA.

It is unclear what impact this delay will have on Boeing's contract to replace the Air Force's aging KC-135s. Both company and service officials said they are continuing to assess the implications.

But there is no question meeting the August 2017 deadline was a key milestone for Boeing. The new tanker is no stranger to schedule slips, but until now the company never backed off its commitment to delivering the initial 18 tankers on time.

The latest delay will allow Boeing more time to implement the solution to a refueling boom loads issued identified during flight testing earlier this year, according to a Boeing statement.

Instead of delivering the first aircraft in March 2017 and the 18th in August, Boeing will begin delivering tankers in August, with the final jet delivered in January 2018, according to Air Force spokesman Maj. Rob Leese.

"Throughout KC-46 development the Air Force remained cautiously optimistic that Boeing would quickly address these issues and meet the original goal," said Brig. Gen. Duke Richardson, Program Executive Officer for Tankers, according to an Air Force statement. "However, we understand that no major procurement program is without challenges and the Air Force remains committed to ensuring all aircraft are delivered as technically required."

The initial 18 aircraft will be equipped with two key refueling capabilities – the refueling boom and the centerline drogue – but without the ability to refuel from pods mounted on the plane's wings, called the wing-aerial refueling pod, or WARP. The WARP systems, which are required to complete full contractual RAA, will be delivered separately in October 2018.

The delay is not due to a functionality issue, but comes down to conformity and qualification testing needed for certification, according to Boeing.

The government will not incur any increased cost as a result of the schedule delay, according to Richardson.

Meanwhile, the Air Force will delay a formal decision to approve production of the new tanker, known as Milestone C, from June 2016 to August 2016.

"The underlying production system remains on track, and Boeing will have more than 18 aircraft through the factory line and in various stages of final change incorporation and certification by August 2017," according to Boeing. "The KC-46 Tanker will play a vital role in America's Air Mobility Forces providing both global power projection and unrivaled global reach for decades to come."

Email: lseligman@defensenews.com

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