Ornithopters were a type of aircraft that used flapping wings to fly.
On Earth, ornithopters were tested but unfeasible, while on other planets, generally with lighter gravity and thicker atmosphere, they were used.
Mordred mentioned the helicopter piloted by Flight Lieutenant Lavel as being like one of the ornithopters on Arthur's World, "but with whirling blades for wings". (TV: Battlefield)
The various intelligent insects of Sentarion used ornithopters. Those used by the universities had special markings to identify them. (PROSE: Shakedown)
Instead of using buses on Ha'olam, they used ornithopters. (PROSE: Seeing I)
Ornithopters were also used on Quinnis. The First Doctor used one whilst on the planet. (AUDIO: Quinnis)