I'm not sure where to post this so please move if I guessed wrong.

I purchased a ticket from ORD to LHR on UAL/BMI. I need to purchase a ticket on the outside BNA-ORD. It will be on AA. I can take a flight that gives me a layover of either an hour and a half or four hours. I'm inclined to take the 4 hour layover as a precaution. I'm not so concerned about the timing coming back as I will choose a 3 hour layover which should be fine and if not there is a later flight. I will be carryon going so that will not be an issue.

Is there anything I should consider? I would love to take the later flight. The trip is in October so weather should not be a big issue. The ticket on UAL/BMI was the Priceline fare that ran last week so I don't know how things would work if I missed a connection. Thanks for any thoughts as I have never booked 2 tickets this way.

I think you've answered your own question. O'Hare is always unpredictable, plus you'll need to change terminals going between AA and UA. I'd take the longer layover if given the choice.

You won't have any issues booking the two tickets from different vendors aside from the (minor) hassle of checking in twice.

If you miss a "connection" between two (different) itineraries, it is a no-show.

What happens depends on the airline issuing the second itinerary, whether you can telephone and make a flight change at the last minute, whether a flat tire rule applies, whether you can stand by for the next flight, etc.

Travel tips: http://members.aol.com/ajaynejr/travel.htm