Depends on what you are flying really. All mil aircraft have a Hirta category that determines how far they must be away from the source. It also lists why you must do it. Autopilots are one favourite but I imagine weapons or fuel tanks might jettison as well. I remember just before I left the RAF the categories went right up which meant, on paper, the Puma couldn't fly the london helilanes or land at any of the main helicopter bases!! If you fly a 152, try and get the CAA to give you some advice!!!
PS. The last I heard, Oakhanger was cancelled???