This most recent overrun is a result of technical problems with the tanker’s complex integrated fuel system, which provides fuel to fly the KC-46 as well as to receivers taking on fuel from a centerline boom or wing-mounted pods. The fuel system is the heart and soul of an aerial tanker, and Boeing’s extensive experience building tankers was a major selling point in its bid against Airbus for the KC-X competition.
That is frankly astonishing. Surely the fuel system would have been one of the very first systems to have been designed for the tanker role?
The A310MRTT has a total of 10 (potentially 11) fuel tanks, with 4 (potentially 5) additional centre tanks augmenting the 6 wing / centre section and tailplane tanks. OK, it doesn't have a boom system as none was specified, but technically it could do so with minor modification to the internal transfer system logic. Operation in the receiver role would also have been possible, but wasn't specified either.
With its large centre tank, the 767-200ER has a much simpler fuel system than the A310-300. The KC-46A has additional centre tank plugs, but even so the aircraft has a pretty simple fuel system compared to the A310MRTT. But maybe that's the issue - with only 1 tank in each wing (excluding surge tanks), plus the centre tank, it would perhaps be more of a challenge to guarantee independent engine feed priority than in the A310MRTT, whose outer tanks can
only feed the engines?
Modifying the wing tank design and fuel feed system for engines and AAR, to provide the same guaranteed engine feed priority as the A310MRTT provides, would be a hugely complex problem at this late stage - and very, very costly.