The plane won’t going to land on US soil but will cross US borders on its route (in the air).
Is “Transiting” applicable only when I have a connecting flight on US ground?
What happens if we have to make an emergency landing in the US?
You need no paperwork for any country in the world (whether the US or not) simply for flying over it. So no, you don’t need an ESTA.
If an emergency landing were to occur, there are specific emergency procedures in place – for VWP nationals, this could involve obtaining an ESTA on arrival.