Bringing guitar on a plane- easy 10 pts?

I've always taken my guitar on the plane in my trans-Atlantic flights to Europe, and I've always flown SAS or LOT, but this year I'm flying AirBerlin and I cannot find any information regarding musical instruments on board. I found a tiny bit but it required directly contacting them 48 hours prior to the flight. I currently have 72 hours and I'd appreciate any responses with information. I'd rather not have them put it under the plane as it is an expensive guitar, but I have a hard case if I must. Please be a specific as possible, all answers appreciated!