Originally Posted by LondonElite

What are your flight times and what day of the week is this? Transferring at LHR (especially the archaic bus transfer between T3 (AA arrival) and T5 (BA NCE departure) can sometimes feel like you've earned a leading role in a Kafka play.

Originally Posted by Efrem

Again for future reference: Fifteen airports outside the U.S. have U.S. customs pre-clearance facilities. Most are in Canada and the Caribbean, allowing flights to small U.S. airports that don't have customs and immigration facilities. Others are at Shannon and Dublin in Ireland and in Abu Dhabi. The list will probably grow in the next couple of years. In those places, you take care of the formalities before take-off and arrive in the U.S. as a domestic passenger.

Originally Posted by BearX220

Congratulations on your trip to Europe. At Heathrow, both coming and going, you will be subject to a TSA-style security check but not customs or immigration. You will not see your checked baggage at LHR; it transfers without your involvement. Your Customs encounter will be (and, generally, is always) in your arrival country. NCE on the way out, ORD on the way home.

This doesn't apply to your upcoming trip but might be useful for future reference: when you are landing in the US, you do customs and immigration at your first arrival city, whether or not it is your final destination. If you were connecting on to OMA from ORD, you would still do customs, etc. at ORD. Most other countries do not work like this.

Originally Posted by LondonElite

You will be in transit at LHR and go through customs and immigration at NCE. Your bags will be through-checked and you won't see them again until NCE. Enjoy your trip!