In an earlier post, I remarked that looking at the crash video, if the speed is about 500mph and the time from horizontal flight to vertical is about 2.5 seconds, a back of the envelope calculation suggests approx 15g initial G.
That's no aerodynamics calculation, purely on the physics of something at a certain speed changing direction in a certain amount of time. 21g may have been a peak figure for a short amount of time.