The FFV capability doesn't activate for the player until you draw your secondary weapon or binoculars, or exits and re-enters the vehicle from the outside.
FFV turn out works if the player initialises in the vehicle via the moveinCommander etc. commands
In a way it's kind of cool that you have to draw a weapon first in order to use FFV from a turned out position, but in circumstances where one might configure a crew member who only has a primary weapon, they may get stuck being unable to FFV <- Using the new select Primary Weapon keybind alleviates this problem.