The scheduled first delivery date for Boeing’s KC-46A tanker programme is imminent, and the US Air Force is at least outwardly retaining a cautiously optimistic view regarding August 2017.

For Boeing, much of the tanker’s story thus far has followed a pattern of two steps forward and one step back. At the 2016 Farnborough air show, Boeing announced a hardware fix for the KC-46, after the aircraft experienced higher than expected axial loads on the tanker’s refuelling boom. The fix marked a mild victory for a programme that has faced several hurdles since its inception in 2011. In April 2016, Boeing took a $243 million hit for cost overruns on the USAF project, though the programme chalked up wins later that July with a successful Fairchild Republic A-10 refuelling and the green light to begin low-rate initial production of Lots 1 and 2 in August. A January report from the Pentagon’s top weapons tester also warned that the KC-46 programme’s schedule was unlikely to go as planned.

In a May roundtable meeting outside Seattle, Washington, Boeing officials told reporters it would deliver the first tanker by the end of 2017, pushing past the air force’s original September delivery date. The USAF announced a KC-46 delivery ceremony set for 15 September in a Federal Business Opportunities notice earlier this year. The service set that as a planning date, Boeing’s KC-46 programme manager Mike Gibbons said this week.

“There’s uncertainty to when that date is,” Gibbons told reporters in May. “The air force was planning on a potential date that could have been as early as September. It’s likely that we will deliver later than that, probably late this year.”

In a 25 May written statement to Congress, the air force’s top uniformed acquisition officials expressed less optimism for the tanker recapitalisation programme’s timeline. Several subsystems and hardware still need approval from the Federal Aviation Administration, which is holding up flight testing, the USAF states.

“The KC-46 test programme is progressing, albeit slower than planned,” the USAF states. “Boeing is several months behind schedule, which means the first aircraft will likely deliver after September 2017.”

Several of Boeing’s test aircraft are also undergoing design changes, slowing down the rate of planned tests. The air force and Boeing will update Congress on the programme’s timeline following an ongoing risk assessment, though the service is committed to August 2017 for first delivery as planned, and the last of 18 aircraft by January 2018.

Boeing still requires an amended type certification from the FAA for the baseline 767 with tanker provisions and a supplemental type certification for the militarised variant. The company is over 90% complete with the amended certification and 60% complete with the supplemental, Gibbons says. The plan this year is to finish the aircraft certification with the FAA and fill out the rest with the air force, which has already completed most of the airworthiness certification with the FAA, he adds.

Boeing will complete final assembly at its Everett, Washington facility, where both the freighter and tanker versions of the 767 widebody aircraft are being built on the same production line. While a refuelling boom issue last May has slowed down development, Boeing maintains overall production is continuing at the same rate. Boeing has 20 aircraft in production today and will start deliveries once development is complete and the aircraft receives its FAA certification.

“Regardless of where we end in development and delivering that first aircraft, we have a number of jets that will then be delivered fairly quickly to the USAF,” Gibbons says. “The air force won’t take them all in one lump. In the first part of 2018, we believe we can get the air force those 18 aircraft.”

Gibbons also played down warnings from a recent Government Accountability Office report that cautioned that Boeing’s test timetable may be unrealistically quick. Boeing is supposed to complete 29,000 total developmental flight test points over a 32-month period, a higher rate than it has previously demonstrated, according to the GAO.

“The difference is, what we’ve got in the last phase is certification, whereas at the beginning of the programme it was actual flight testing for development and learning,” Gibbons says. “In the first part of flight testing, anything we learn and do, often would require software tweaks or even hardware mods and when that happened, slowed the pace of testing.”

The last phase for certification entails proving the aircraft’s stability, as well as final production versions of hardware and software already examined during flight tests, he adds.

Boeing has six aircraft in testing, including one tanker undergoing electromagnetics effects (EME) testing at Edwards AFB, California. That testing includes the full tanker and its Cobham wing aerial refuelling pods (WARPs), though Cobham’s design still requires FAA certification.

“The FAA certification requires that we go in with a production unit that has been witnessed by the FAA to be built as a production unit,” Gibbons says. “But that EME test is ongoing right now to be a full-up aircraft system test.”

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Boeing plans to certificate 64 receiver aircraft as part of Phase 2 certification for the tanker and has already refuelled the F-16, F/A-18, AV-8B, C-17 and A-10. Gibbons expects that number to grow as more operators come on board and the USAF makes a determination of which aircraft the service wants to certificate. Phase 2 receiver certification will last through 2018 and will address 70% of the USAF’s refuelling operations today. Phase 3, which the USAF will conduct and Boeing will support, will certificate additional receiver aircraft including the F-35.

President Donald Trump’s proposed budget requests $93.8 million for the ongoing KC-46 engineering, developing and manufacturing, as well as $2.6 billion to award 15 aircraft for low rate initial production Lot 4 in January 2018. That procurement would support the USAF’s plan to buy 179 KC-46 tankers by fiscal year 2028, which still accounts for just a portion of the service’s ultimate recapitalisation of the legacy tanker fleet. There are more than 400 tankers in the USAF’s current fleet today and the service is planning two more recapitalisations, KC-Y and KC-Z, to replace the remainder of its aging KC-10s.

In the future, Boeing sees growth in the KC-46’s communications relay mission and is planning more automation for the aircraft’s tanking mission.