smooth in their responses to varying wind shear or gusting wind conditions – i.e., not able to compensate in all dimensions rapidly enough – to safely permit their use. The first aircraft to be certified to CAT III standards, on 28 December 1968, was the Sud Aviation Caravelle, followed by the Hawker-Siddeley HS.121 Trident in May 1972 (CAT IIIA) and to CAT IIIB during 1975. The Trident had been certified to CAT II on 7 February 1968. Autoland capability has seen the most rapid adoption in areas and on aircraft that must frequently operate in very poor visibility. Airports troubled by fog on a regular basis are prime candidates for Category III approaches, and including autoland capability on jet airliners helps reduce the likelihood that they will be forced to divert by bad weather. Autoland is highly accurate. In his 1959 paper, John Charnley, then Superintendent of the UK Royal Aircraft Establishment's (RAE) Blind Landing Experimental Unit (BLEU), concluded a discussion of statistical results by saying that "It is fair to claim, therefore, that not only will the automatic system land the aircraft when the weather prevents the human pilot, it also performs the operation much more precisely". Previously, autoland systems have been so expensive that they were rarely used on small aircraft. 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. History Background Commercial aviation autoland was initially developed in the United Kingdom, as a result of the frequent occurrence of very low visibility conditions in winter in North-west Europe. These occur particularly when anticyclones are in place over central Europe in November/December/January when temperatures are low, and radiation fog easily forms in relatively stable air. The severity of this type of fog was exacerbated in the late 1940s and 1950s by the prevalence of carbon and other smoke particles in the air from