Unsupported flight

"And then Harry saw him. Voldemort was flying like smoke on the wind, without broomstick or thestral to hold him, his snake-like face gleaming out of the blackness, his white fingers raising his wand again —"

- Harry Potter witnesses the first known instance of a wizard flying unsupported.

Unsupported flight is a spell that allows a witch or wizard to fly without the use of a broomstick or other form of support. It is different from levitation, which only allows one to hover a few feet off the ground and does not allow for movement. Long thought to be a magical impossibilty, this spell was invented by Lord Voldemort sometime around 1997.

Early attempts
"No spell yet devised enables wizards to fly unaided in human form. […] Levitation is commonplace, but our ancestors were not content with hovering five feet from the ground. They wanted more. They wanted to fly like birds, but without the inconvenience of growing feathers."

- Kennilworthy Whisp, Quidditch Through the Ages.

Attempts to fly unaided have been made by wizards since ancient times. Levitation has been possible at least since the invention of the Levitation Spell in ancient England, and an attempt to improve upon this and achieve true flight made by Jarleth Hobart in 1544 led to the invention of the Levitation Charm. The flying broomstick, which allows wizards to fly with relative ease and convenience, was invented around 962 A.D., and seemed to satisfy most wizards' desire to fly. True, unaided flight of a human being, however, was long considered an magical impossibility.

Invention
Sometime prior to 1997, Tom Riddle succeeded where other wizards had failed and managed true flight. He first publicly showed off this ablity during the Battle of the Seven Potters, using the spell to great effect and almost managing to defeat Harry Potter if not for a odd reaction with their wands. He also taught this spell to Severus Snape, who used it to safely escape from Hogwarts shortly before the Battle of Hogwarts. Also, in the film version of The Deathly Hallows: Part 2, numerous death eaters were seen escaping using this spell after Harry Potter was revealed to be alive.

Behind the scenes

 * In the Harry Potter films, Apparition is often depicted as similar to flight, with those using it even able to cast spells, physically fight, and affect the stability of the Millennium Bridge mid-"flight". As it is portrayed in the books, however, this sort of application of Apparition would be impossible, and thus this cannot be considered canon.
 * Non-beings, such as Dementors and Poltergeist, can fly through the air without any form of physical aid.
 * Ghosts are capable of flight without any physical supports.
 * In the film adaption of Harry Potter and the Philosopher's Stone, Quirinus Quirrell was flying without any visible support towards Harry in the last of the seven Underground Chambers, most likely due to Voldemort possessing him.

Appearances

 * Harry Potter and the Deathly Hallows
 * Harry Potter and the Deathly Hallows: Part 1
 * Harry Potter and the Deathly Hallows: Part 1 (video game)
 * Harry Potter and the Deathly Hallows: Part 2
 * Harry Potter and the Deathly Hallows: Part 2 (video game)
 * LEGO Harry Potter: Years 5-7
 * Quidditch Through the Ages
 * Wonderbook: Book of Spells