(Bloomberg) -- The Air Force has stopped accepting deliveries of Boeing Co.’s new refueling tanker aircraft for the second time in a month because of debris found in closed compartments, according to Secretary Heather Wilson.

The halt in deliveries of the KC-46A Pegasus is latest issue to plague the $44 billion effort to create the first U.S.-built flying gas station for the Pentagon’s fleet since the KC-10A Extender in 1981.

"We actually stopped again," Wilson said Tuesday in response to Representative Joe Courtney, a Connecticut Democrat, during a House Armed Services Committee hearing. Wilson told lawmakers that the Air Force found "foreign object debris" in closed compartments of the aircraft.

The decision to halt acceptance was made on March 23, Air Force spokeswoman Ann Stefanek said afterward in an email.

The first two KC-46 tankers were sent to a U.S. Air Force base in Kansas in January, a milestone that nonetheless couldn’t eliminate uncertainty about next steps in the program, including the delivery of the first batch of 18 planes, two spare engines and nine sets of wing-mounted refueling pods. Those were all initially due in August 2017, but final delivery could slip by more than three years, according to the Defense Contract Management Agency.

“Resolving this issue is a company and program priority –- we are committed to delivering” debris-free aircraft, Boeing spokesman Charles Ramey said in an email. “Although we’ve made improvements to date, we can do better.”

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