In Assassin's Creed Brotherhood, Leonardo da Vinci builds Ezio a machine called the Flying Machine.
The Flying Machine is based on Leonardo's earlier glider designs and appears during a mission in which Ezio uses it to attack Borgia forces in Rome. The sequence expands on the flying-machine mission from Assassin's Creed II, where Leonardo creates a device that lets Ezio fly over Venice.
Brotherhood presents Leonardo as an inventor whose work is controlled and weaponized by Cesare Borgia. Ezio destroys several of Leonardo's war machines after recovering them, including devices based on historical designs. The Flying Machine is therefore part of both the game's historical-fiction setting and its recurring conflict over technology.
The answer is often confused with the game's broader category of Leonardo's war machines. Those include multiple devices, while the Flying Machine specifically refers to the aircraft used in the aerial mission.