Originally Posted by
Fat Clemenza
...savings made with fleet commonality will always overcome fuel issues
I don't think I'd be so blatant about it. There are certain exceptions to this, and (to cite an example) at one time Delta had nine engine types going through their shop - and they were regarded as something of a paragon of efficiency. But that was long ago.
If your route is so diverse as to seriously limit the productivity of a plane on certain routes (Hot, high, short airfields with obstacles,....) then a second type is worth a serious look.
