Cant seem to get it to work...........

I have a trigger set for some Dorniers to spawn. The trigger is a air group entering an area and I see the Hud message but no dorniers spawn?
Code:
public override void OnTrigger(int missionNumber, string shortName, bool active)
{
base.OnTrigger(missionNumber, shortName, active);
if ("DoSpawn".Equals(shortName) && active)
{
AiAction action = GamePlay.gpGetAction("DoSpawn");
if (action != null)
{
action.Do();
}
SendScreenMessageTo(Blue(), "Dorniers request Escort: Boulogne,(H,5) Alt:3500M, 10 mins ! ");
GamePlay.gpGetTrigger(shortName).Enable = false;
}
}