If you are flying (alone or with a dead gunner)in a attak heli,
you can't aim with the gun as pilot in "manual fire"-mode.
i think there should be a capabilty to do this.
the freelook could be a good solution (pseud TADS/PNVS system).
choose gun as weapon
press alt for freelook
OR press alt only for freelook
and a special key-combination(alt + shift) for the link gun with freelook
look at your enemies position