Flights out of San Carlos

Our itinerary is still coming together and we do not want to commit yet to buying a ticket to fly out of San Carlos because we are not sure if we will stay in this area for longer or want to leave to explore more northern areas. My question is, are the flights usually full from San Carlos to Managua on Thurs and Sun? Can you purchase a one way ticket in San Carlos say the day you would like to fly out?

I flew from San Carlos to Managua in January 2012 and had no problems buying the ticket the same day and the flight was not full. The flight was beautiful and was worth the money for the time saved.