I decided to use my Saitek X52 controller to pilot the helicopter. I used the built-in Arma 3 profile for the controller and started playing. I immediately noticed that the analogue throttle was inverted and looking into the controls, I found that the Collective raise (analogue) setting was set to "Saitek X52 Z Axis+" while the Collective lower (analogue) setting was set to "Saitek X52 Z Axis-". I decided to invert the settings and the throttle worked properly.

It would be useful (to make configuring easier) if the mapping reflected the change I made, as I am sure most people do not plan to fly a helicopter with an inverted throttle.