The KC-135 Stratotanker has four engines. Why go to a platform with only two engines?
Cheaper to operate.
Those two engines put out lots more power than the 50ish year old designes on the KC135. And the are far easier to maintain.
The A330 has two engines. The A340 uses the very same fuselage and wings, but has four engines. The A330 outsells the A340 10 to 1 because it’s cheaper to operate. The A330 has more than adequage one engine out performance.
Why go with four engines with it’s added expense, complexity, and operating costs?
I haven’t researched the contract in depth so I’m not sure. My guess would be that, generally speaking, more engines means less efficiency (which is why airlines prefer twins).
The Boeing 767 based proposl only has two engines, so what’s your point? Two big engines are less expensive and cheaper to operate.
Because if they had asked for 4 engines, The only contender could have been the Airbus A340.
Boeing and its tame politicians would have started whining sooner.
You can even glide about 65 nautical miles without any engine.
http://en.wikipedia.org/wiki/Air_Transat_Flight_236
In that incident the number of engines was irrelevant.