Is it possible to cancel flight ride?

Yes and no.

You can not get off a taxi while it is traveling between flight nodes. This is very much by design as the taxi can not be used as a substitute for a flying mount.

However, if your destination travels through another flight path node (as indicated on the taxi map as a "flying boot" that intersects the line between you and your destination) than you can choose to instead land at that node (that is, get off at the "next stop"). To do this, simply click the "Request Stop" button (located near the bottom-left of your action bar) while in transit. You'll land at the next flight node instead of your destination.

Note: using this method, you will only be billed for the flight nodes that you reached - saving you some gold.