In the past, it has been generally accepted internationally that in order to land aircraft in runway visual ranges below 400 metres—ICAO Category 3 conditions—a fail operational automatic landing system is required. The Trident aircraft with its triplex system is of course an example of this philosophy. However, the overall system requirements for such operations were specified nearly a decade ago and considerable advances have been made since then on such aspects as understanding fog characteristics, avionic system design, visual aids and of course, airline experience of all-weather operations. Consequently, there is now a world-wide interest in trying to ease the system requirements without jeopardising safety, for example, by considering the use of less complex fail-passive autopilots. If feasible, this would allow existing suitably equipped aircraft to operate to lower minima and hopefully, widen the spectrum of aircraft capable of being equipped, with overall benefits in terms of increased regularity and hence revenue.