The AMA National Model Aircraft Safety Code says in the control line section paragraph #1 "I will subject my complete control system (including safety thong where applicable) to an inspection and pull test prior to flying".

Now if we procede to the AMA Competition regulations for 2004 in the controlline chapter, Control Line General paragraph #4 Safety Thongs. It states: "A safety thong connecting the handel of the control line models to the pilots wrist, and strong enough to prevent accidental release of the model, shall be worn at all flights of control line events except all racing events"

From the above the above I would infer that for sport flying a thong is not required but is at all controlline competive events with the exception of control line racing events.

Having said that I cannot see any reason not to use one all the time on anything more potent than a Cox plastic, which I do. Very simple with only the need to drill a little hole in your handel and a piece of leather bootlace.

John