While speed is a factor, it isn't the only factor. The altitude at which they are unlocked matters as well. Moving at Mach 1.0 at a lower altitude could subject

While speed is a factor, it isn't the only factor. The altitude at which they are unlocked matters as well. Moving at Mach 1.0 at a lower altitude could subject the plane to far greater forces than at Mach 1.4 at a much higher altitude, where the air is thinner. Furthermore, where the force is coming from probably also plays a role. The angle of the force applied to the feathers may change when the force is not coming from a fall, but is instead the result of the engines provide force from behind the fuselage.