Philip Reeve 
Web of Air 

In a faraway corner of a ruined world, a mysterious boy is building a flying machine. Birds help him, and so does a beautiful, brilliant, half-human engineer called Fever Crumb. But powerful enemies stalk them — either to possess their revolutionary invention, or to destroy the secrets of flight forever. The breathtaking new story from the awesome world of MORTAL ENGINES. Award-winning writer Philip Reeve creates an extraordinary new city of moving buildings and human birds in a classic novel that is sure to thrill fans young and old.