I've been playing GTA V (story mode, PS4) and I'm at about 40% completion. I've googled helicopter locations, and gone to all of them (hospital near Franklin's house, N.O.O.S.E, helipad for purchase, etc.), but there is never a helicopter present. I've tried these locations with different characters, too.
Do I need to unlock them somehow? Will they spawn after a certain mission, etc.?
Thanks in advance, and let me know if you need any more info.