In either Michael & Franklin's helipads or Trevor's?
I tried to land a buzzard (the gunship) in Trevor's, but his frogger was blocking it up. Then when I moved that, and "stored" the buzzard. It seemed to glitch, and I lost the buzzard.
Also, similar question about planes. Trevor's hanger only holds one plane... that can't be right can it?
I presume either I'm doing something daft, or there's a problem.