[Huliwang]

Think he never flew on that bird. The bird is larger than a man but never flew in the novel. Always walk based on what I remembered.

That was the early part where that bird taught Yang Kuo its previous master's kungfu. After mastering all the techniques, he left with that bird to roam the jiang-hu. I think that was when he started flying around on that bird but was not written in the novel. 
However towards the end, he appeared with "small dragon girl" zooming in from the sky sitting on that big bird to save the last daughter of Kuok Jing who was tied to a burning platform by that Fahlun Master.....