Leonardo was fascinated by the phenomenon of flight for much of his life, producing many studies, including Codex on the Flight of Birds (c. 1505), as well as plans for several flying machines, such as a flapping ornithopter and a machine with a helical rotor. A 2003 documentary by British television station Channel Four, titled Leonardo's Dream Machines, various designs by Leonardo, such as a parachute and a giant crossbow, were interpreted and constructed. Some of those designs proved successful, whilst others fared less well when tested.