Boeing's KC-X fuel-savings claim is interesting, but dubious

Boeing's KC-X fuel-savings claim is interesting, but dubious

I’ve really been scratching my head over Boeing’s press release yesterday that claims the 767-200ER enjoys a 24% fuel efficiency advantage over the Airbus A330-200. The statistic is not trivial, as it could be a huge factor in the evaluation for the US Air Force’s KC-X tanker replacement contract.\nBut the statistic would seem – to me, anyway -- to be counter-intuitive. Airbus designed the A330-200 a decade after the 767 entered service. The whole point of the A330 design was to offer a more efficient aircraft in roughly the same passenger class.\nAirlines clearly believe that Airbus has the more efficient aircraft, voting with their airplane orders heavily in the A330’s favor over the past decade. The A330 continues to be popular in the commercial market, even despite facing the hugely successful (marketing-wise) 787. By contrast, orders for Boeing’s 767 have slowed to a trickle, and it’s reasonable to argue the production line wouldn’t exist without the potential of the KC-X contract.\nBut, upon further study, Boeing’s claims appear to have some statistical merit, but also some serious potential flaws. To make sense of it, you just have to look at the performance statistics a little differently for a tanker than you would for a passenger aircraft.\nAn airliner carrying a maximum passenger load is not carrying anywhere near its maximum lifting capacity. For example, the 767-200ER’s empty-weight plus a maximum payload of passengers, luggage and cargo adds up to about 270,000 pounds. \nHowever, the same aircraft stuffed with fuel instead of passengers is certificated to lift a maximum of 395,000 pounds. The total amount includes the weight of the aircraft (184,000 pounds) and the weight of the “useful load” of fuel (211,000 pounds).\n[All of my statistics come from Boeing’s report.]\nLooking at the statistics this way would seem to give the 767-200ER a clear advantage over its rival. The Airbus designed the A330 to be optimized for a growth version of the aircraft, so the -200 proportionally carries more “empty weight” (265,700 pounds) than the 767-200ER. This means there is proportionately less “useful load” available to carry fuel (248,065), factoring in the A330’s larger overall size compared to the 767.\nBut Boeing’s claim of a 24% fuel advantage rests on a dubious (perhaps even ridiculous) assumption, at least to my thinking. That statistic appears to assume that the US Air Force will operate the tanker at a maximum “useful load” of fuel on every takeoff for the next 40 years. \nIn fact, I would argue it’s more reasonable to assume the future tanker will almost never takeoff at the aircraft’s maximum gross takeoff weight, whether it’s the 767 or the A330. \nThis means Boeing’s entire statistical analysis is useless as a reasonable measure of operating performance, although it does raise an interesting point that in theory the tanker version of the 767 can be more efficient than the tanker version of the A330. I’d like to see Boeing re-compute the numbers, but this time using reasonable operating assumptions.