Door gunners in the UH-80 have issues with engaging infantry and vehicle targets when told to Engage At Will.
Oftentimes they will not engage at all, leaving you a sitting duck. Other times, they won't engage, but then once you're 2km away they'll start shooting at targets out of their effective range.
From testing, it seems, at least for the ghost hawk, tied to the rather small range of motion of the miniguns, combined with very poor aiming skills and very small spread of the miniguns.
Create player as pilot UH80 with AI gunners in the editor. Fly over large group of infantry. Especially happens in urban areas, where they won't fire at all. In open areas (I tested in the salt flats), they will engage, but will only fire in 5 round bursts or so, but will not hit hardly anything. This is on max AI skill.
Additionally, they will not fire if the aircraft is moving very much - you need to be almost in a hover for them to shoot. Forward motion more than 15-30km/h seems to prevent all firing.
The AI call out targets, but refuse to engage infantry the majority of the time. They seem to be better about engaging vehicles, but it's still spotty. I've done a slow orbit around a town with a single AI infantry squad and my gunners don't fire a shot, and the ghost hawk eventually is downed by small arms fire. I tested further to see if AI pilots fared any better, and if they would assign targets and have gunners engage, but they do not - the AI ghosthawk was shot down faster, and engaged exactly zero targets.
This is extremely annoying, as it currently means that the ghosthawk is useless in any sort of engagement capacity, and is only good for dropping folks off.