Rudder Boost
Just in reference to the above post and not to the accident. I was once conducting a pre-buy survey C of A test flight on a B200. I was not rated so had a rated guy fly the aircraft. When I shut down the right engine, at altitude, the rudder boost ran away in the wrong direction towards the failed engine. The pilot flying, a normal type rated pilot, did not cope and I recovered the aircraft when I took control from him at an extreme attitude. However it was controllable if you are sharp. The fault was a capillary hole in the rubber boost valve membrane so it acted like a venturi and the rubber membrane was sucked rather than pushed.