However, as display technology has developed the addition of a head up display (HUD) allows for a trained pilot to manually fly the aircraft using guidance cues from the flight guidance system. This significantly reduces the cost of operating in very low visibility, and allows aircraft that are not equipped for automatic landings to make a manual landing safely at lower levels of look ahead visibility or runway visual range (RVR). In 1989, Alaska Airlines was the first airline in the world to manually land a passenger-carrying jet (Boeing B727) in FAA Category III weather (dense fog) made possible with the head-up guidance system.[3][4]