Originally Posted by
IAHtraveler
If both flights are on the same day/similar time from different starting points, I'd be very surprised if CO's system doesn't catch it. They know that your butt cannot be in 2 cities at the same time and they can cancel either/both of the tickets.
You brought up an interesting point. Somehow, if CO system can monitor the flights that I am on during the day of travel and, based on what you wrote, will cancel both itineraries, why is it that the reservation system will not detect a new booking that is in conflict with an existing one? Are there two separate systems for CO? It seems like their reservation system will allow you to book another itinerary even if it is a duplicate with the same dates and flight numbers. In fact, I just did hold a new duplicate reservation and CO rez system accepted it. It looks like the double booking fail-safe check on CO system is implemented during the day of travel, not during the time of reservation where it is selling you tickets.
UA's .bomb and AA.com will not let you do this.^^