The May 2013 yaw-induced control incident aboard a Sikorsky S-76 at the London-area Denham airfield was caused by the failure of a metal sealing ball inside the pedal damper trim actuator, according to a UK Air Accidents Investigation Branch report issued last week. During arrival, the Sikorsky’s autopilot disconnected on its own and caused the helicopter to begin yawing to the right, which the pilot attempted to correct before ultimately making a safe landing.