A a privately operated Pilatus PC-24 aircraft was involved in a loss of control accident near Kelowna, BC, Canada. The Pilatus PC-24 had departed Vancouver International Airport (CYVR), BC, for an instrument flight rules flight to Kelowna Airport (CYLW), BC. After passing FL240 while in the climb at 280 KIAS to the selected cruise altitude of FL270, the flight crew felt a brief shudder followed by a loud bang. The aircraft yawed to the right, nosed down and began to accelerate. The pilot-in-command retarded both engine thrust levers, applied left rudder pedal, and requested the second-in-command to apply nose left rudder trim in an attempt to correct the sudden yaw. Attempts to control the yaw with rudder trim were unsuccessful. Aircraft control was passed to the second-in-command. Directional control was achieved by reducing airspeed and applying differential engine thrust while both pilots applied pressure on the left rudder pedal. The flight crew advised Vancouver Center of the flight control difficulty, declared an emergency and requested that airport emergency services stand by for the landing at CYLW, where the aircraft landed without further incident at 2139 PDT. Neither pilots, nor the passenger were injured. Company maintenance conducted an initial inspection and found that the rudder mass balance weight arm had broken off and became lodged in a position that prevented full movement of the rudder. Further inspection found that the rudder trim tab control rods had become separated aft of the rudder trim actuator.