engineOn works fine for vehicles, but for helicopters, it's only able to turn the engines on. chopper engineOn false; will do nothing.
Currently I'm resorting to this work-around:
MTP_fnc_engineOn =
{
private ["_vehicle", "_on"]; _vehicle = _this select 0; _on = _this select 1; if (!(_vehicle isKindOf "Air")) then { _vehicle engineOn _on; } else { if (_on) then { _vehicle engineOn true; } else { _vehicle spawn { private ["_vehicle"]; _vehicle = _this; _fuel = fuel _vehicle; _vehicle setFuel 0; sleep 0.1; _vehicle setFuel _fuel; } }; };
};