Check this script as well.
add in init line of a helicopter-
togglesmoke = [this] execVM "addsmoke.sqf";
Place addsmoke.sqf and popsmoke.sqf in mission folder.
addsmoke.sqf
//addsmoke.sqf
_heli = _this select 0;
sleep 1;
dropsmoke = _heli addaction ["drop smoke","popsmoke.sqf",true,1,false,true,"","driver _target == _this"];
popsmoke.sqf
//popsmoke.sqf
_bird = _this select 0;
_pilot = driver _bird;
_smoke = createvehicle ["SmokeShellGreen", [1,1,1], [], 0, ""];
_smoke attachTo [_bird, [-0.6,2,1]];
sleep 3;
detach _smoke;
_pilot sidechat "smoke dropped!";