Avatar Aang had a lot of responsibilities on his shoulders. Unlike all those who came before him, Aang found himself in a unique circumstance. Not only was Aang the Avatar, but he was also the last of his nation. While previous incarnations of the Avatar were able to detach themselves from their nations and become the beacon of balance that they were expected to be, Aang had to hold on to his identity as an Air Nomad, which he was the last remaining vestige of.
A new theory has emerged that Aang was likely able to tap into a fraction of a forgotten Airbending technique, one that was revived in full during the time of his successor Avatar Korra, by Zaheer, a member of the terrorist organization called the Red Lotus. While flight is not an ability most Airbenders can conjure without bending the air around them, the theory suggests that Aang might have almost unlocked this ability before Zaheer.
Aang almost rediscovered flying in Avatar: The Last Airbender
When he was unable to access the Avatar State, Aang decided to train with Guru Pathik, a mystic who would teach Aang about opening the seven Chakras that might allow him to access the Avatar State.
However, when it came to unlocking his seventh Chakra, Aang was asked to let go of all earthly attachments, freeing himself completely. This, while helping him unlock the Avatar state, could have also had him rediscover the ability to fly, which also requires the wielder to be rid of Earthly detachments.
When Aang learns of his friends being in trouble in Ba Sing Se, he rushes to protect them, and in the fight that ensues with Azula and Zuko, Aang encapsulates himself in an Earth tent, meditating to open his seventh Chakra, which we can assume he does since he enters the Avatar State. During this brief second, Aang is shown to be rising from the ground, hovering even, without using any particular airbending. However, he is promptly shot down by Azula, almost killing him.
Azula almost ended the Avatar Cycle
While Aang was in the Avatar State, Azula was able to shoot the Avatar down with her lightning bending, which put Aang in a near-death situation. While it was not revealed at the time, Legend of Korra taught audiences that if the Avatar was killed in the Avatar state, the cycle would seize, and the power of the Avatar would leave the physical world.
Without knowing it, Azula could have secured the ultimate victory for the Fire Nation if she had managed to kill Aang. Since Aang was in the Avatar state when he lost consciousness, had he died, the Avatar cycle would come to an end. This would mean that no new Avatar would be born for the next 10,000 years at least.
The only way the Avatar could return is if Vaatu, the spirit of light that resides in the Avatar, would return (which she would, emerging out of her sworn enemy Raava), and would decide to bond with a human being again, re-establishing the Avatar mantle. However, until that happened, the world would be soundly under Fire Nation rule, all thanks to Azula. And to think that she decided to give this honor to Zuko, the one person she considered the weakest in the family.
