Check with your airline first. Even then, it's a toss up.
I flew from LGA (New York) to Shannon (Ireland). On the way out I put my board in the overhead and it was not an issue. The TSA agent at security was stoked that I longboarded and we chatted for a bit about it.
When I was coming back I got shit from the security guy and had to turn around and check my longboard. Longboards count as blunt weapons. When I got to NY my board was all scuffed up.
I would recommend checking it in the first place and finding a safe way to check it. It depends on how long your board is and who you're traveling with.
My deck was 37" and I was flying aer lingus.