The Heli Gunner is a Field Order reward on the map Behemoth. When called in, the player spawns in a UH-60 Blackhawk helicopter which can be controlled by the player. A Minigun is also included with the field order, allowing massive firepower from outside of the map. The player can be shot off the helicopter, similar to the Helo Scout.
While the minigun may be powerful, its accuracy makes it a problem, especially when moving around. The Juggernaut Recon/Assault/Maniac combo could be useful for this without the worry of being easily shot off. Steady aim can help with the accuracy significantly. However, using Juggernaut combined with the Heli Gunner can still be risky if health/armor condition ends up low.
Same with the Helo Scout, the gunner will be dropped off at a point of the map (mostly the players team spawn area), sometimes making the drop off extremely dangerous if the area isn't clear, as an enemy player could run to the landing zone and kill the player as they jump off. But unlike the Helo Scout, all targets are shown up with a red-orange square and still is active when slowing down to drop off so better awareness of the routes is crucial to survival.