Boeing Co. charged the Japanese government an "excessive” price for some spare parts for its refueling tanker plane, as much as 16 times more than the U.S. Air Force paid for its latest versions, according to a service assessment.

In one example involving an April $79 million spare parts contract for the KC-46 tanker, Japan was billed for navigation lights made by subcontractor Honeywell Inc. "at a unit price more than 1,500% above the previous unit price,” according to the previously undisclosed Air Force summary prepared last month.

From November 2019 until March of this year, the U.S. Air Force tried, without success, to "secure adequate pricing information” from Boeing to determine whether the price for the lights and other parts in the package was fair and reasonable under federal regulations, according to the summary.