will detect that there is a difference in the commands and this will take both computers off line (fail-passive) at which time the flight crew must immediately take control of the aircraft as the automatic systems have done the safe thing by taking themselves off line. During system design, the predicted reliability numbers for the individual equipment which makes up the entire autoland system (sensors, computers, controls, and so forth) are combined and an overall probability of failure is calculated. As the threat exists primarily during the flare through roll-out, this exposure time is used and the overall failure probability must be less than one in a million. See also LAAS Instrument landing system Head-up display Fog References External links BOAC VC10 Automatic Landing 1968 Canberra automatic landing at RAE Bedford, 1958 Trident Autolanding a 1969 Flight article on the Hawker Siddeley Trident's autoland system Automatic Landing a 1969 Flight article on the differing philosophies regarding autoland requirements "All-Weather Landings" a 1953 Flight article about the BLEU "Smiths Autoland System" 1 1965 Flight advertisement for the system Aircraft landing systems Avionics