Originally Posted by rickair7777

Yes.



The main factor actually was the requirement that you have three or more engines for extended over-water ops. When ETOPS relaxed that requirement to two engines, the trijet was done.




Two engines are more efficient...

- Less rotating-machinery drag (saves energy).

- Fewer support systems (saves weight).

- Less flow energy-loss (no long s-duct).

- Larger fans are actually more efficient anyway. The core is going to be a little bit heavier, but it can optimized for max fuel efficiency at cruise speeds vice T/O.

If the weight and fuel savings were not enough, the reduced Mx cost (by 33%) seals the deal.