WASHINGTON — The US Air Force is reviewing Boeing's schedule for its KC-46 tanker to ensure the recapitalization program is still on track to meet a critical deadline as repeated setbacks threaten to derail the company's tight testing schedule.

Despite eating an $835 million pre-tax charge that stemmed from development issues with the integrated fuel system on the plane, as well as repeated delays of the first flight, Boeing is bullish about its ability to deliver 18 ready-to-go tankers to the Air Force by August 2017.

"Boeing is committed to delivering the initial 18 tankers by 2017 and we continue to talk daily with the Air Force on our progress," Boeing spokeswoman Caroline Hutcheson said Aug. 25.

But the Air Force needs more convincing, Secretary Deborah Lee James indicated on Monday during a press conference at the Pentagon.

"We're in the process of going over the schedule again to see whether we can see our way clear on that as well," James said. "Certainly, the margin in the schedule is all but gone at this point."

In Boeing's most recent challenge, first flight of the tanker test plane was delayed by about a month because a mislabeled chemical was mistakenly loaded into the aircraft's refueling line during testing, according to the spokeswoman. The company's most recent estimate for timing of first flight is late August or early September — a shift of almost a year from the original time line.

If problems with the integrated fuel system tank persist, or if the delay in first flight sets back the overall test schedule, the Air Force is concerned the program could see a domino effect. Boeing must successfully demonstrate the required refueling capabilities during flight tests before the Pentagon will certify the program, an official stamp of approval the Air Force hopes to get between January and April of 2016.

"The other thing that we will be taking a look at is, would there be any operational impacts?" James said. "Should they not make that August of 2017 contractual deadline, would that have any operational impacts on us, and, if so, would there be any contractual considerations that we should look at?"

The good news is, the Air Force is not on the hook for any further cost overruns, James said.

The Air Force is locked in for 179 tankers under its KC-X recapitalization program, which is planned to be the backbone of US air refueling efforts for the coming decades.

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