Just weeks before the planned first flight of a fully outfitted KC-46 Air Force tanker, the plane’s fueling system has been damaged by a chemical mix-up, temporarily grounding the jet. Meanwhile, Boeing put veteran executive Scott Fancher in charge of the troubled tanker program.

In a new setback just weeks before the planned first flight of a fully outfitted KC-46 Air Force tanker, the Boeing plane’s fueling system has been damaged by a chemical mix-up, temporarily grounding the jet.

The jet — the first test plane outfitted with working air-refueling systems and designated as a tanker — was at the fuel dock on Paine Field last week when mechanics used the wrong chemical during a test of the fuel system, according to people familiar with the details.

The chemical, supplied by a vendor and mislabeled, caused corrosion and damaged the fuel system, including the advanced new fuel boom designed to offload gas to fighter aircraft, the sources said.

The fuel boom as well as the auxiliary fuel tanks in the fuselage of the airplane have been removed from the aircraft for inspection and any necessary repairs. The Air Force has been informed of the incident.

Boeing spokesman Chick Ramey would not provide details but confirmed Boeing is “determining a plan of action” for “an emergent KC-46 issue.”

“We are currently assessing the potential impact of the issue on scheduled program activities,” Ramey said.

It’s unclear how much this incident will delay the plane’s first flight, which was expected in late August or early September.

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