Q. I ended my visit to another city earlier than I expected and wanted to take an earlier flight back home on the same day as originally scheduled (my original flight was to depart at 5 p.m. but I attempted to take a12 noon flight). However, United wanted to charge me the same change fee ($150) that I would pay had I changed the day or week of my flight.  I thought I could go standby for an earlier flight for free, or at least that used to be the policy. Do all airlines charge to standby for an empty seat on an earlier flight on the same day?

A. U.S.-based airlines have slightly different policies regarding same day flight change fees. They used to allow standing by for a different flight on the same day for free, but no more. Most airlines charge $50, and only allow confirmed same day changes rather than standby. United charges $75, Jetblue charges $40. Most airlines require that you make your change request no more than three hours before flight time (in other words, if the flight you wish to change to leaves at 5 p.m., you cannot make your change request earlier than 2 p.m.). Southwest is a bit different in that it doesn't charge to make same day changes (or any changes for that matter); however, if your original fare was $59 and there are no more $59 seats available on your requested new flight, you will have to pay any fare difference. However, sometimes airlines will waive same day change fees if it suits them, especially if your original flight is delayed or cancelled (or if show up at the gate minutes before the flight and there's no time to collect the fee). And Jetblue will let you standby for the flight immediately preceding your original one for free.