Q. Is it true AA has a rule that if I miss a flight due to a mishap (accident, traffic, flat tire, slept in, etc.) they'll put me on the next flight without change fees and original and new flight fare difference?

Maybe. Kind of. Yes and no.

The so-called "Flat Tire Rule" is formally called Late Arrival Standby, and is extended to domestic passengers who show up at the airport within two hours of scheduled departure. They will be accommodated on a standby basis free of charges if they can depart the same day.

They may enhance their chances by paying $75 (waived for Executive Platinum) for
Domestic Same Day Flight Change if it's available.

Q. What happens if my plane hasn't left, but I'm past the check-in time requirement?

You're probably still going to have to take the consequences. You must check in an hour prior to scheduled departure for international flights, and at the gate 30 minutes prior to scheduled departures; if you're late, you're late.

Q. What happens if I'm on an international flight?

Standby is not allowed for international flights. If you can get International Same Day Flight Change you may be OK to destinations SDFC is allowed (on the same day, of course). You will generally pay the change fee associated with your original fare plus the difference between your original fare and the "walk up" fare charged passengers booking today.

(JonNYC and ThreeJulietTango say Canada, USVI and Puerto Rico flights are exceptions, as are any destinations you can buy SDFC on (no standby internationally). See post at TravelingBetter.com: http://goo.gl/S3CAq4 and post #89 for this and other exceptions, including itineraries with domestic and international sectors (the fare break is at the domestic to international connection).

Q. What if my flight was the last one of the day / there's no flight with an available seat that can accommodate me the same day?

You will generally pay the change fee associated with your original fare plus the difference between your original fare and the "walk up" fare charged passengers booking today.

Frankly, booking the last flight of the day entails some risk. If there are delays and IROPS, they often get later and later as the day progresses, and in the situation at issue here means no standby, likely significant costs to you and meal and lodging costs added to your expenses.

Q. Can I just use my mobile and call?

No; you're actually expected to show at the check-in counter within two hours. But, calling can prevent your itinerary from being cancelled because you were listed as a "no show" when you miss the flight, and if you have status it's possible you could have some arrangements made for you on the spot - less to do at the check-in counter.

Q. That's not fair! Can I do anything?

Check to see if your credit card (e.g. Citi AAdvantage Executive MasterCard, etc.) includes trip interruption insurance, or buy it in advance of your trip.

Or, if you don't want to purchase TCII "self-insure"; set aside some money for unforeseen circumstances knowing if you travel frequently you'll probably encounter travel disruption.

Thanks to JonNYC, Linda Burbank of USA Today and gemac for clarification.