I realize that the attempt in starting this thread was to discuss the "design" philosophy of two engines vs. three; however, there is one point that hasn't been made and it's the reason tri-jets are not being manufactured anywhere in the world today. There is no market for them because of the cost of the third seat; i.e., the third pilot.

Rickair7777 is correct about the overall efficiencies of today's fuel efficient fan engines. When one can manufacture a high bypass fan that produces 125,000 lbs. of thrust and is as fuel efficient as the new GE engines are, the discussion is over !

Have a bodacious day Mates