There are three daily flights between most of the cities the airline serves:
Puerto Plata Santo Domingo (the smaller airport, not Las Americas) Punta Cana
The schedule changes slightly for the Santo Domingo/Puerto Plata route two days per week when the flight makes a stop over. I'll post further details when I get the schedule in front of me. I'm sorry but I don't have it with just now.
I know the one way fare between Santo Domingo and Puerto Plata is 700 pesos and there is a roundtrip reduced fare that applies when the outbound and return segments occur on the same day.