The elevator control restriction was caused by the failure of the elevator autopilot servo control cable, which failed due to cyclic fatigue. The slack in the broken cable wrapped around the elevator autopilot servo mount in such a way that it was bound between the servo mount and the servo mount cable guide pins. The bound cable interfered with the rotation of the servo mount, which remained connected to the aft side of the elevator control quadrant by the intact aft cables. This condition resulted in the limited rotation of the elevator control quadrant in one direction.