Domestic to international connections at Mexico City Airport
 

My wife and I might be flying Aeromexico from Merida to San Francisco in February, with a tight 45 minute connection in Mexico City. For what it's worth, we'd be in business class with just carry-on luggage. We're US passport holders. It would be an early morning connection on a Sunday, arriving in Mexico City at 8:15 am and departing 9 am.

Is that at all a realistic connection? And if we were to miss it, how good is Aeromexico likely to be about getting us on a later flight?

Thanks for any advice.

Being on a Sunday morning helps as there's less traffic. It looks like that MID-MEX flight is on a 737 all Sundays in February, so this helps too because these planes should arrive directly to the terminal. Embraer planes would more likely be parked at remote positions and passengers bused into the terminal, making the first-to-deplane advantage almost useless in that case.

On-time performance for that early MID-MEX flight is very good even on weekdays, also consider that AM pads MEX flight schedules a lot and you might actually land well before 8 AM, so even if they switched aircraft for an Embraer you should be good. I'd say that odds are very much in your favor of making the connection though maybe with a bit of fast walking, as you're more likely to arrive to the south side of the terminal and depart from the north side.

But anyway there isn't much margin for the odd weather or mechanical delay so better plan for that just in case. AM has a later flight to SFO and they should have no problem putting you there unless it's full; however, if you absolutely need to be in SF by Monday morning, I'd suggest you check in advance the alternatives you might have including flying AM to LAX or TIJ instead (even Sacramento or Fresno via GDL) and get to SF on your own from there, or buying another ticket out of MEX on another airline. Just in case you need to make arrangements there so you already know what to look for.

This is all very useful, sw3. Thanks so much!

I just had another question: Would we have to go through Immigration in MEX or Merida? And assuming it's MEX, would that slow down the process a lot?

Traveling from MID to SFO via MEX?

You'll go through Immigration once you land in SFO.

There is no immigration 'preclearance' process in Mexico -- this only happens when departing Canadian airports for the U.S. (plus some airports in the Caribbean, Ireland and UAE). From anywhere else in the world, i.e. Mexico, you go through CBP clearance when you land back in the U.S.

Your Mexican tourist card will be taken by airline staff when you board your SFO-MEX flight.

Thanks! I guess I mean: Would we go through Passport Control upon leaving Mexico, but I gather from your post that it's just a matter of handing in our tourist card.

Correct-ish. There's no secured international departure area, just like the USA. The boarding agent will take your card along with your BP.

Thanks!

MEX / Domestic to Int'l on Separate PNR (Aeromex)
 

Looking to book a flight from SJD-MEX, MEX-IAH on separate PNR's, both Aeromexico, with a ~2.5 hour layover. This is a legal connection since Aeromexico offers it direct, but it is cheaper to book the segments separately. If i am travelling with luggage, will I be able to check bags straight through to IAH when I check in at SJD? Are there any Covid/customs issues that would potentially cause me to have to collect luggage and re-check in MEX? J is not much more than Y if that makes a difference. Thanks

No COVID/Customs issues, but you're at the mercy of the SJD agent checking the bag through. (Also, there may be separate baggage allowance policies for the two flights, which is a potential issue.)
Also, some national flights have been arriving T1 - not sure if SJD has become part of that mess, so you may want to check that out. It is a "not so convenient" inter-terminal connection, although I believe there's now an airside bus. I've been through MEX twice recently, but have not had the pleasure of an inter-terminal connection.

And given all things AM, I'd want to be on the same ticket in case of IROPS. If anything goes wrong with SJD/MEX, AM isn't going to help you get to IAH, and AM, historically, isn't going to be very sympathetic with your now missed MEX/IAH segment. I wouldn't expect anything more from AM than letting you use whatever fare you paid on that ticket as credit for the full last minute fare, plus an airport "live person ticketing" fee.

Maybe I'm wrong, but that would be my expectation after two years of canceled flight nonsense and credits, rebooking, and so on over the past two years.