Let us assume, for the purposes of the question, that by 'turn' we mean a change in heading or direction. In that case, if the aircraft's wings are level with the horizon a turn can be achieved only by yawing the aircraft around its normal axis (which is at 90° to the horizon). On the other hand, if the aircraft is at 90° angle of bank a turn can be achieved only by pitching the aircraft around its lateral axis (which is at 90° to the horizon). Consequently, if the aircraft is in a banked attitude between 0° and 90° any turn must be a combination of pitch and yaw.