I think it depends on the loads - they are a charter airline, right?
I mean, the Danish charters who are flown by MYT, can often change equipment from week to week. A good example could be, that when my dad & his girlfried went to the Canaries, they flew out on a A320, but returned the next week on a A330.
Thanks. I guess the same goes for Air Transat. The travelled called the other day to inform us of the flight changes with our flight to Punta Cana on the 29th. Now we are stopping over in Puerto Plata and then continuing over to Punta Cana. I appears that Air Transat is only sending one plane down to The D.R. this summer a week and passengers going to La Romana are being bussed down from Punta Cana Airport. I really hope that Air Transat switches back the flight to the A310 or upgrade to the A330 but I doubt it might happen.