We are not talking about secret military bases here. Nothing at a civilian airport is classified! (except for the immigration area, they don't like cameras there).
I take my digital SLR with me almost every time I preflight my airplane, all over the world, in case there is something to take a picture of nearby. Nobody has said anything to me, nor has any sign or anything else indicated that it is illegal to do so. Only in the CIS do they frown on it, but even there, I've done it openly in some airports on a few occasions, and the security guys who were watching have never said anything about it.
I'd love to see someone tell me that I can't take a picture of the airplane I myself just flew. Common sense must prevail.