Adventure; Young Adult Literature; Sci-Fi
This is definitely a story of adventure: they're shipwrecked twice, attacked by pirates, held captive by said pirates, escape to beat the pirates… and all while trying to provide proof of a brand-new species that has never been discovered before on an uncharted tropical island. If that's not adventure, then we're not sure what is.
And we know we're on young adult lit turf for certain because not only does the book prominently feature young adults (go figure), but it is also oriented toward a young adult audience. Romance is limited to a first-kiss, the language is pretty accessible (ship terminology aside), and the characters are the same age as the intended readers (which makes them easily relatable).
Finally, Airborn could be classified as science fiction, since many of the things in the story most definitely do not exist in real life. Hydrium—unfortunately—is not a real element, airships would be an inefficient way to travel, and cloud cats do not exist (well, they don't to the best of our knowledge, at least…).