This was an incredible video I took in an American Eagle descending into Dayton earlier this summer. At Noon during descent the aircraft exceeded its critical Mach number. And sections of the airfoil where exceeding Mach 1. This is completely safe, just a cool way of seeing a shock wave when the sun is directly above the plane.
Note the line near the quarter cord of the wing. You can see the density gradient as the light from
The sun is bent towards the higher density of the shock.
