Well, if you only trust AM and MX, the God bless you in your journey to low fare land. By the way, AM and MX drop their fares just after Aviacsa started it. Aviacsa created the beautiful "Tuesdays only belong to Aviacsa". That is the name of their promotion and the date they release the promotional fares. Of course, after some time, Aviacsa increased its load factor and AM and MX as the great number two´s started to follow that little and profitable airline (AM and MX are in red numbers) called Aviacsa to try to generate more revenue and increase their already low load factors. So now you know when you can get the promotional fares from almost every mexican airline. By the way, aviacsa has never had an incident and AM and MX have had tons of them. Good luck on your way to Merida.