This Lord of the Rings theory has come to light online, and has proved very popular. It claims to answer the question of why the eagles didn't just fly the ring to Mordor.
However, there are some issues with the idea – and fair warning, it's pretty long.
We've summarised the basic theory here:
There are actually reasons why the eagles never carried the ring, though they are less exciting. Firstly, the Fellowship was attempting to remain out of sight of Sauron. Giant eagles are not that subtle.
The eagles are also a sentient race, not a group of animals – and definitely not a Middle-earth Uber to be called at will.
There was also a pretty massive orc army, with arrows that had brought down eagles in the past.
Oh, and the Nazgûl on their fell beasts.
And aside from the tactical reasons, Frodo alone had been given the responsibility of carrying the ring by the Council of Elrond, meaning it could not be passed on to the eagles.
Even if they were just carrying Frodo, who was carrying the ring.
With thanks to khyeili.tumblr.com, Ask Middle Earth, u/Shagomir, the LOTR Wiki, and the many, many other people who have written about this topic.
It's worth noting that the user who posted the original theory, VulcanDeathGrip, freely admitted his knowledge of the books was limited, and certainly didn't claim the theory was accurate.