Airline economics are a bit complicated. What exactly constitutes "below costs"? Let's say I have a plane flying from A->B that is typically 90% full, and a pla

Airline economics are a bit complicated. What exactly constitutes "below costs"? Let's say I have a plane flying from A->B that is typically 90% full, and a plane flying from B->C that is typically 90% full. You want to get from A to C. The cost on my end for doing this is already a sunk cost - I can carry you for a very small marginal cost. If someone else is willing to do it for $200, I'll do it for $190 (Hell - I'm willing to go very cheap - maybe even $50), because getting something for those seats is better than getting nothing. What I don't want to do is to let someone else's fare on route A->C cause me to lower the price for people who want to fly from A->B (whose alternative is to pay $250).