However, the analysis in the U.S. Defense Department report was based on historical data from military development programs, whereas the KC-46A program schedule is based on Boeing Commercial Airplanes' more aggressive approach to testing.
"The KC-46 development test program is aggressive but achievable," Air Force spokesman Ed Gulick said in a statement responding to the report by the Pentagon's chief weapons tester.
The Air Force last year assessed the risk of falling behind schedule and found "that Boeing has a greater than 90 percent probability" of delivering 18 aircraft and support services by August 2017, as required by the contract, according to Gulick.
The report released Wednesday said that the program schedule doesn't allot enough time for Boeing and the Air Force to finish development testing and early crew training before starting more advanced testing.
But the program's approach, called "Test Once," addresses that issue by using each test event to check as many required criteria as possible, according to Gulick.
Also, several Boeing and subcontractor test labs are being used to troubleshoot potential problems before they crop up, according to Boeing officials.
The KC-46A is also not a clean-sheet airplane but rather a derivative of the Chicago-based company's popular widebody commercial 767-200ER jetliner.
The program's four test planes are all in production at Boeing's Everett facility, and most testing will be done at Boeing Field in Seattle.
"Our current assessment confirms that we have a valid flight test plan in place and that we remain on plan to deliver the first 18 combat-ready tankers to the U.S. Air Force by 2017," the company said in a statement.
The Pentagon report also raised other concerns, including problems with the radar warning system and the plane's vulnerability to fire in certain circumstances.
The Air Force, Boeing and subcontractor Raytheon, which makes the plane's radar warning system, are addressing the issues.
Early test data indicate that the contract's specifications leave the plane vulnerable to fires in empty fuel bays, according to the report.
Adding a fire-suppression system could require congressional approval, depending on the cost.
The Air Force has ordered 179 of the planes as the first stage in modernizing its tanker fleet. Boeing has to deliver the first 18 tankers by 2017 and churn out 15 a year through 2027. The contract for the first 18 planes is worth about $4.4 billion, with Boeing responsible for any research-and-development overruns.
The Pentagon's efforts to award a contract to replace its aging tankers had two earlier bidding rounds by Boeing and Airbus invalidated and led to an ethics scandal ending with Boeing officials being sentenced to prison in 2004.
Dan Catchpole: 425-339-3454; email@example.com.
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