ORLANDO, Fla. — Boeing’s deliveries of its KC-46 tanker to the U.S. Air Force have been suspended as the service investigates a series of problems with foreign object debris, its top acquisition official confirmed Friday.

Will Roper, the service’s assistant secretary for acquisition, technology and logistics, told reporters that it will likely be “some time” before the service begins accepting new tankers from Boeing.

“I was able to get some data from our team on the foreign object debris that’s being experienced on the KC-46 line. It’s still to be determined how extensive and how far into the production line it goes,” he said.

“It boils down to process, culture and leadership in making systems. A trip to Boeing is almost certainly going to be necessary for me to approve DD250s again,” he added, using the Defense Department’s term for accepting an aircraft.

During a Thursday afternoon roundtable with reporters, Roper said that the Air Force had grounded planes for about a week due to concerns about tools and other foreign object debris left in the aircraft — a potential safety hazard. The issue was first reported by The Seattle Times.

Roper said then that early feedback from the Air Force’s on-site team seemed positive, and that the approval of two tanker deliveries was expected Thursday evening.

On Friday, Roper clarified that at that point he hadn’t talked to the Defense Contract Management Agency, Air Mobility Command or other stakeholders about the way forward, but after those discussions took place the Air Force opted to delay aircraft deliveries.

A memo obtained to The Seattle Times pointed to a series of foreign object debris, or FOD, incidents caused by workers leaving tools inside the aircraft, with eight incidents documented on planes moving through production and two occurrences in KC-46s delivered to the Air Force.

Roper didn’t say whether there were other signs that FOD control at Boeing’s Everett, Washington, production plant had degraded, but offered that the Air Force was still whittling down a root cause and wanted to more fully understand the scope of the problem.

“Drawing from history and past programs with FOD, sometimes it’s a major issue. Sometimes is a minor issue,” he said. “In this case it’s not clear how extensive the root causes are. And if you’re uncertain, in the case of safety issues, you play it conservative. So, no reason for us to accept airplanes until we’re confident.

“I can’t be very specific on the remediation, but I just have enough reason for concern not to go forward accepting the aircraft.”

The Air Force and DCMA have identified 13 process improvements that it is directing Boeing to put in place, and they will finalize that corrective action plan later in the day, he said Friday. Boeing will be responsible for paying for any fixes that are put in place, and the company has also offered to inspect the aircraft already delivered to the Air Force.

Boeing delivered the first KC-46 to the Air Force in January, and so far six tankers have been accepted by McConnell Air Force Base, Kansas, and Altus Air Force Base, Oklahoma. However, various technical problems delayed the program, and the delivery of the first tanker occurred almost two years later than expected.

“The real downside is not a cost issue. This isn’t costing us anything. It’s the lack of training. We need aircraft for pilots and operators to train,” Roper said.

A spokesman for Boeing said the company continues to work with the Air Force on the tanker delivery schedule.