These failures occurred on the 'Radical'-style heel piece. The top portion of the binding, including the heel pins, separates from the lower portion of the binding. In the most recent failure, it appears that the failure initiated with the two screws connecting the top plate to the lower portion of the heel piece.
|Intact Heel Piece on the Right|
I believe the two screws failed, and then the rear portion of the binding plastic failed due to the upward force on the heel pins
Dynafit was one of the most significant skiing innovations in my lifetime. But, the failures described in this post, and other failures not described here, indicate that we need a more robust, yet still lightweight, binding/boot system for alpine touring.