The bus runs from Fethiye otogar direct to Dalaman airport calling at domestic & international terminals depending on season. Check
www.havas.net website for timetable, the buses leave approx. 2 1/2 hours before the departures of Turkish Airlines flights, If you are flying with another airline check if you will arrive in good time for check in & departure.
It takes 1 hour to get to airport and the bus will pick up en route-in Gunlukbasi, on the main Dalaman road, Gocek etc.
If you are arriving into Dalaman the buses will be waiting (again timed for domestic arrivals-check website for these times too) outside the domestic terminal and will then pick up at the International terminal depending on season.
There is also a service to/from Marmaris.
It is a great service, very reliable and good value at 10 TL per person