Q: Tom, are most airlines universal in their standby flight rules? If you get to an airport early and there is an earlier flight, is there usually a charge to change your flight? -CG

A: Standby travel leaves me with sweaty palms and acid reflux, CG. Every seat in the departure could be empty and cloaked in cobwebs, and I'd still stew over not getting on a flight as a standby passenger. While 'confirmed' is one of my favorite travel words, here are some other things to consider.

As with most airline policies, there is not a standard or universal rule for standing by, each airline varies. The first thing to know is standby usually applies to the return leg of the trip and on the same day as originally planned. When you change the day or the outgoing portion of the itinerary, additional airline charges apply in most cases.

Of course, I have experienced the universe-is-perfectly-aligned-today moment when exceptions and customer service prevailed in my favor, but like a solar eclipse, frequency of such an occurrence is rare.

When flights are lightly booked, you're usually standby cleared at check-in and given a seat. When flights seem full, check with the agent. It may be money well spent to confirm your seat and avoid further delay.

Generalities aside, here are specific rules for same-day changes by airline and links to the full page text:

American Airlines
You can get a confirmed seat for same-day flight changes for domestic travel on all fares for a $35 fee. Passengers can call Reservations or handle the transaction at the airport ticket counter or Self-Service Check-In machines. If eligible seats are available within 12 hours of departure of alternate flights for your same itinerary, your flight change can be confirmed. Also, American continues to offer the same-day option of standing by for an earlier or later domestic flight for eligible fares at no charge. Read more.

Continental Airlines
The confirmed seat fee when changing your flight for travel on the same day is $50. The same-day change option is available on Continental Airlines, Continental Express and/or Continental Micronesia. Changes may be confirmed within three hours of your new desired flight at any airport check-in kiosk or with an airport agent. You may also contact Continental Reservations by phone. Read more.

Delta Air Lines
The same-day confirmed option allows you to change your flight time on the same day of travel for a fee of $50. To use the same-day confirmed option, you must confirm your new flight within three hours of the scheduled departure time. Flexible fares such as refundable tickets may be exempt for a change fee. Read more.

Northwest Airlines
Customers may make same-day domestic flight changes for a $25 fee on qualifying flights. This option is available on the scheduled day of departure at the time of check-in for a flight with the same origin and destination either earlier or later than the original flight. Previously, the option was limited to flight changes within three hours of check-in or the original flight. Read more.

United Airlines
Checking in and standing by for an earlier flight is allowed on the same day of travel without paying a fee. Seat confirmation is available for $75 with check-in online or at a kiosk at the airport on the same day of travel within 3 hours of the time of your request. Read more.

US Airways
You may move up to any earlier flight on the same day of your originally scheduled departure time at the airport (with the exception of flights to Hawaii and Europe). You can only make day-of-departure changes at the airport. If there is an open seat available on any earlier flight that departs on the same day as your originally scheduled departure, you may change to that flight and we will automatically confirm your reservation for $25 for flights within the 48 contiguous United States and $50 for flights to Latin America, the Caribbean, Canada and Alaska. Read more.