A new (March 21) airworthiness directive (AD) for the Cessna 560XL was prompted by reports of jammed or stiff rudder control due to water freezing on the rudder bias cables and pulleys in the tailcone. The directive requires modification of the drain installation of the tailcone stinger on the aft canted bulkhead, inspections for drain holes in the forward and aft frames, and modification of the drain holes. Ice accumulation on the cables and pulleys can result in jamming of the rudder and reduced controllability of the airplane.