Why don't aircraft have a choice of engine size?
I can't believe there is always one correct thrust rating for a jet transport. Surely the lower the power/lower the cruise speed, the lower the fuel used. The higher the power/cruise speed, the higher the number of sectors per day per hull/per crew hour. Even if there is a sweet spot at any given moment, that must change as prices change over time? So why do we never see engine power choice, or engines varying over the life of a model?