Spirit Airlines mulls tying fees to flight demand

The complex world of airlines fees might soon get even more confusing.

Spirit Airlines is considering tying its bag and seat-assignment fees to demand. On a peak travel day, for instance, the fees could be higher than they are now. But on a slow afternoon, passengers might catch a break. The changes wouldn't happen for months, meaning passengers are safe this Thanksgiving and Christmas.

Spirit did not say how much higher, or lower, the fees might be. CEO Ben Baldanza says the changes are something Spirit executives have been thinking about but haven't yet agreed to.

United Airlines and Delta Air Lines already price some seats with extra legroom at different levels based on the demand for that flight. No airline currently does that with luggage fees.