Atlanta-based AirTran in June began charging customers for advance seat reservations on discounted fares -- something Northwest Airlines started last year. United offers "economy plus" seating, with extra legroom , at no charge -- but only to their frequent fliers.

And on Southwest, the only large domestic airline with no pre-assigned seats, seniors may find themselves in the least desirable spots due to the company's group boarding policy.

Travel experts say playing around with seat assignments is just one more way that carriers are looking to differentiate themselves from their competitors as well as generate some extra revenue.

Get the full story at the South Florida Sun-Sentinel