The feline righting reflex refers to their natural ability to orient themselves as they fall in order to land on their dainty, agile feet. The amazing righting reflex starts to show up at 3–4 weeks of age, and is perfected at an astonishing 7 weeks of age. Cats are able to do this because they have an extraordinarily flexible backbone and no functional clavicle. The minimum height required for this to safely take place in most cats would be around a foot. Tailless felines also have this ability, since a cat mostly moves its hind legs and relies on management of angular momentum to set up for landing, and the tail is in fact little used for this accomplishment.
After a quick but accurate formative of down from up visually with their vestibular apparatus, cats manage to wind themselves to face downward without ever changing their net angular momentum. They are able to achieve this by bending in the middle so that the front portion of their body rotates in relation to a different axis than the rear half, then tucking their front legs in to decrease the moment of inertia the front portion of their body and extending their rear legs to increase the moment of inertia of the rear portion of their body so that they can spin their front half as much as 90° if so needed, while the rear half turns in the opposite direction as little as 10°. Depending on the cat's litheness and initial angular momentum, if any, the cat may need to repeat steps two and three one or more times in order to complete a complete 180° rotation.
In addition to the righting reflex cats have many other features that will decrease damage from a fall. Their diminutive size, light bone structure, and thick fur lessen their terminal velocity. In addition, once righted they may also spread out their body to amplify drag and slow the fall to some degree. A falling cat's terminal velocity is 60 mph while that of a falling man in a free fall position is 130 mph. At terminal velocity feline’s also relax as they fall, which protects them to some level on impact.
Even with this amazing God-given ability, injuries still occur and it is your responsibility to protect your cat from dangerous falls.