I never played AC2, but there has always been some give in determining if a crash was lethal. I AC4 you could "ride" along the ground and ocean at 0ft. You could also scrape your wings against walls in the tunnels, and it wouldn't an instant death. I remember AC5 being the least forgiving out of all of them, though.
Yo buddy, Still alive? -Solo Wing Pixy, Ace Combat Zero