Boeing, U.S. Air Force Successfully Test KC-46A Boom Fix

 - July 18, 2016, 12:05 PM
The KC-46A Pegasus successfully refuels a C-17 Globemaster III on July 12. (Photo: Paul Weatherman, Boeing)

Updated with Air Force announcement of completed A-10 demonstration

Boeing and the U.S. Air Force successfully tested a hardware fix to resolve a boom loading issue they experienced during refueling exercises with the KC-46A Pegasus tanker. Resolving the issue is a prerequisite to the Air Force’s planned decision to approve low-rate initial production (LRIP) of the tanker in August.

The KC-46A connected in flight with an F-16 Fighting Falcon on July 8 and with a C-17 Globemaster III on July 12, the Air Force said. Those flights supported the “Milestone C” decision to begin LRIP, a decision the service will make after the tanker successfully makes contact with and transfers fuel to several different aircraft types.

The KC-46’s telescoping, fly-by-wire refueling boom is derived from the boom used on the KC-10 Extender. In late May, the Air Force postponed the LRIP decision from June to August to address what it described as “higher than expected axial boom loads” experienced during a refueling exercise with the C-17.

On July 13, the service said that unexpected boom loads were first detected during successful testing with an F-16 earlier this year. “These loads were again present during the initial attempt with the C-17 and necessitated installation of hydraulic pressure relief valves in the boom,” the Air Force stated.

Meeting with reporters on July 10 in advance of the Farnborough Airshow, Boeing Defense, Space and Security president and CEO Leanne Caret said the manufacturer is “well into” testing a hardware solution to the problem.

“We had a software solution to work the boom axial load condition, which as you extend the boom in free air, especially as we are looking at large aircraft, there was some instability that we needed to address,” Caret said. “That [software] solution didn’t prove as beneficial and so we switched at the end of May to a hardware solution that we had been working in parallel and that is showing great progress.”

Boeing said the hardware fix involves installing two bypass valves to relieve the pressure of fuel loading on the boom. Flight-tesing on the engineering and manufacturing development 4 prototype tanker started in early July.

The manufacturer has also been delayed in certifying the KC-46A’s centerline drogue system and wing aerial refueling pods, which are supplied by Cobham. Caret said there was no change to the program schedule as announced in May.

“We have been flying and we are seeing positive results,” Caret said. “I feel very confident in this solution. As always we are in a test program; we have 70 percent of our flight-test [program] in front of us, so I remain pragmatic but I am pleased with the results we are seeing.”

The Air Force expects to conduct the final refueling test using the boom with an A-10 Thunderbolt II this month. (On July 18, the service said the KC-46A completed all flight tests required for the Milestone C decision three days earlier by offloading 1,500 pounds of fuel to an A-10. The five other required aerial refueling demonstrations were with the C-17 and F-16 using the boom, the Navy's F-18 Hornet and AV-8B Harrier II using the centerline and wing drogue systems, and the KC-46 as a receiver aircraft.)

“Once complete with the A-10, we will request approval from Mr. Frank Kendall, under secretary of defense for acquisition, technology and logistics, to award production Lots 1 and 2, totaling 19 KC-46A aircraft,” said Darlene Costello, Air Force service acquisition executive.