One thing we do know is that they have been mentioned in ancient texts dating as far back as the Book of Isaiah, and the Mayan civilisation also talked about Flying Serpents. Were the Mayans even talking about the same thing that we class as a Flying Serpent today. Or something completely different.
Here is a picture of a Flying Serpent taken in December 2003. The person that took the photograph was on a plane flying from Los Angeles to Singapore.