WASHINGTON – Although Boeing has largely addressed early development problems with its KC-46 tanker, a government watchdog is warning the company has a challenging road ahead to complete testing, deliver the required number of aircraft to the US Air Force, and get the planes FAA certified.

Test officials believe Boeing's test schedule for the KC-46 program is "optimistic," according to an April report by the Government Accountability Office. The program office projects Boeing will need an additional four months beyond the August 2017 target to deliver 18 full-up tankers due to testing and parts qualification issues, the report states.

The Air Force and Boeing were forced to revise the original test and delivery schedules due to three major development challenges: wiring design issues, redesign of several components of the aerial refueling system, and a fuel contamination accident in July 2015.

Boeing now plans to deliver four production aircraft to the Air Force to begin operational testing in May 2017 — a year later than originally planned, according to GAO. The company will then deliver all 18 production aircraft — two more than it originally planned to deliver in this timeframe — to the Air Force over the six months leading up to August 2017. Operational testing will be completed about two months after the aircraft are delivered.

This concurrency risks late discoveries of problems with the planes, which Boeing must fix on its own dime, GAO cautioned.

Using company resources, Boeing recently started building the first low-rate initial production aircraft, spokesman Charles Ramey noted in an April 11 email.

"Boeing still expects to meet the August 2017 RAA. We are making steady progress in flight test and aircraft production and are confident we are taking the right steps to fulfill our commitment to the Air Force," Ramey said, adding that the company will "continue to take a hard look at the schedule for opportunities to incorporate efficiencies and lessons learned."

The Air Force is planning a "Milestone C" decision to formally approve production of the new tanker in May, according to the service. However, a technical problem that occurred during a recent test could delay that milestone, Defense News reported earlier this month.

Additionally, the GAO points out Boeing has not yet obtained FAA approval of two key aerial refueling systems: the centerline drogue system and the wing aerial refueling pods, which were built without following FAA processes. Boeing now projects these components will be ready for the FAA to certify by July 2017 — over three years late.

In the meantime, Boeing was approved in January to begin testing the KC-46 developmental aircraft without the two aerial refueling components being fully qualified. This will allow the program to proceed with most of the KC-46 certification testing, according to the report.

Still, due to these and earlier delays, Boeing will not be able to complete development of the aircraft until June 2018, according to GAO — five months later than required.

"Boeing has solved many of its early manufacturing problems and has taken steps to mitigate potential schedule risks," GAO wrote. "However, the company has a challenging road ahead in testing and delivering aircraft in a compressed amount of time."

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