Contrary to popular belief, cats don’t always land on their feet.
If cats fall a short distance, they can usually right themselves and land on their feet. They have very small collarbones which allow them to fit through small spaces and their backbones are very flexible, more so than other animals. Their spines have about 53 loose fitting vertebrae (humans have 34) and more elastic cushioning than most other mammals. With their front legs freely moving they have the ability to twist as much as 180 degrees and turn with their feet and legs absorbing most of the impact on landing. By the time a cat is 7 weeks old, it is able to perform this feat.
Cats have help from their inner ears which act as gyroscopes. They are able to change positions so that when falling at high speeds, their legs can absorb the impact of falling.
However when falling from more than one floor up, a cat can sustain severe and sometimes fatal injuries. Falling from such heights, their legs cannot absorb the impact and other parts of the body hit the ground.
In any case, you don’t want your cat falling even a short distance.
If you live in an apartment house or have upstairs porches and allow your cat the freedom of the balcony, there are precautions you should take. Have these areas screened in if possible. If your cat is allowed on the balcony, have it harnessed and leashed on a short leash. However if you leash your cat, I would not recommend leaving it out on the balcony alone or at least check often that all is well. Check windows and screens to make sure that they are secure. Make any repairs necessary as soon as possible.
The best safety policy is not to allow your cat access to these areas unless they are safely secured.