Boeing’s grand plan to deliver 18 operational KC-46 Pegasus tankers in six months instead of fourteen has been labelled “optimistic” in a new report by the US Government Accountability Office (GAO).

Setbacks encountered during testing in 2014 and 2015 have already delayed the US government’s KC-46 low-rate production decision by nine months from August 2015 to May 2016. Now, the GAO reports that the five-month operational testing phase, which was due to begin in April, will now start in May 2017.

“Boeing will not be able to complete development activities until June 2018, five months later than required,” the congressional watchdog states in its annual appraisal of the KC-46 programme.

The GAO quotes government test officials who say that Boeing’s drive toward 18 aircraft to meet the contractual “required assets available” milestone is “optimistic” and carries four months of "schedule risk". That's not accounting for acknowledged troubles with boom refuelling the massive Boeing C-17 transport, which was meant to happen in January.

“If the air force exercises its options for production lots one and two, any future delays may affect Boeing’s ability to deliver all 18 operational aircraft by August 2017, but that risk is being measured in months rather than years,” the report states.

Those 18 aircraft were meant to include the four developmental aircraft, brought up to an operational standard, plus the first 14 low-rate production examples. Now, the 18 aircraft will include two of the original test aircraft and 16 production line examples, or two more than expected, GAO explains. Because those aircraft will now be delivered before operational testing is complete, Boeing will be financially responsible for any late design changes or fixes.


Boeing KC-46 receives fuel from a US Air Force KC-10


Boeing carries plenty of financial risk as it executes the remaining portion of the tanker development contract, which is a fixed-price deal that caps the US government’s liability at $4.9 billion. As of December 2015, Boeing and the USAF programme office “estimated that Boeing would incur additional costs to complete development of the aircraft of about $769 million and $1.4 billion, respectively”.

As well as stumping up the cash for overruns, Boeing is self-funding construction of the first batch of operational tankers in anticipation of government contracts for seven and 12 aircraft, respectively.

GAO notes that Boeing is also opening a second finishing centre, where it modifies 767-2C freighters into the military-standard KC-46 type.

For the government, at least, the cost of KC-46 development, production and associated military construction has come down 7%, or $3.5 billion, from $51.7 billion to $48.2 billion. The air force is buying 179 tankers as a first step toward replacing 455 Boeing KC-135 'Stratotankers', which average 55 years of age and are maintenance-intensive.


KC-46 wing aerial refuelling pod (WARP) demonstration


GAO notes that Boeing has resolved most issues encountered to date, and is moving past the unfortunate missteps that delayed the type's first flight from early to late 2015 and drove up costs.

There are still problems, however, with certifying the aircraft's centerline drogue system and wing aerial refueling pods.

Those key components should have been ready for Federal Aviation Administration certification in 2014, but won’t be certificated until “July 2017, over 3 years later” because the supplier didn't follow FAA processes during construction.

“To help mitigate schedule risk, Boeing obtained FAA approval in January 2016 to begin testing the KC-46 developmental aircraft without the two aerial refueling components being fully qualified," GAO says.

To date, Boeing has refuelled the F-16, F/A-18, AV-8B and has received fuel from a KC-10. It must still refuel the C-17 and A-10.