My wife and I are going to fly from the U.S. to Brazil in a few weeks, with plane changes in Mexico City both ways. Southbound, we will arrive from Houston on an evening Aeromexico flight and leave 3 1/2 hours later on an Aeromexico flight to Sao Paulo. On our return flight we will arrive on a morning Aeromexico flight and leave on Aeromexico to Denver 4 hours later. It has been decades since I was last in the Mexico City airport. I have three questions: 1. Will we have to go through immigration and customs between flights or is there a provision for international transit passengers? 2. We will be flying in Aeromexico business class. Can anyone tell me about their business class lounge there, what facilities it offers etc? 3. Any suggestions for transiting the Mexico City airport would be welcome.