Frontier and Volaris no longer codesharing?
 

I haven’t been able to book a codeshare flight on volaris through frontier for several months now. At first the flights appeared, but showed no available seats. Now they’ve disappeared altogether (as in, I can’t even search routes like DEN to GDL). I spoke with someone in June who said they were temporarily unavailable, but no other info appears anywhere when searching.

Anyone have any leads?

Likely due to the FAA downgrading Mexico's safety rating. This article calls out that Delta can no longer sell Aeromexico flights so I would assume Frontier and Volaris are subject to the same regulations.

That’s really interesting - thanks for the info. Yeah, that must be what it is. The article says the last time this happened it lasted for 4 months. Will be interesting to see how long this one lasts.

You might try booking through Volaris. They are still showing codeshare connections with Frontier flights.
Just out of curiosity, what is your use case for booking a F9/Y4 codehare flight? The fares were not very competitive from what I saw and the only time I ever used it was to book a Y4 flight via Concur coming back from a work trip (the Y4 flight wasn't listed under their code in Concur, my company's standard for booking work travel). It ended up being a pain since I couldn't checkin online and an agent in GDL had to call someone to manually fix my reservation. Volaris is a neat niche airline and we don't see much discussion about them here.