Despite earlier assurances that Boeing would deliver the US Air Force's first 767-based KC-46A tanker by the end of this year, boom scraping issues and a slew of uncompleted test points may delay delivery until 2018, the head of its Air Mobility Command has revealed.

More than half way into testing, the USAF has discovered severe flaws on the tanker, known as “category 1 deficiencies”. Among the most glaring, the tip of its boom has on occasion struck receiver aircraft outside their refuelling slipways. Boeing engineers are working to fix the problem, but unless the issue is resolved it could delay a scheduled 1 December delivery, Gen Carlton Everhart said at the annual Air, Space and Cyber conference near Washington DC.

It is unknown at this point whether Boeing will be able to meet the USAF’s "required assets available" milestone scheduled for October 2018, Everhart adds.

At the same time, Boeing is still working through test points that will grant the KC-46A's amended type certification from the US Federal Aviation Administration for the baseline 767 with tanker provisions, and a supplemental type certification for the militarised variant. A US Government Accountability Office report released earlier this year warned that if test points were not completed at the planned rate, the already revised delivery schedule for the KC-46A would be "optimistic at best".

“We’re running into a crunch period right now, where we may not be able to get all the test points done,” Everhart says. “Boeing could get this thing accelerated, it could all fall together. What they’re trying to do with their type certification is do parallel certifications.”