Up to that stage the Autoland system had been realised only as a "single-lane" or single channel system, without any redundancy to protect against equipment failure. During the late 1950s and early 1960s increased cooperation between BLEU, the UK Civil Aviation Authority (CAA) and companies in the aviation industry with BEA and BOAC led to the definition of safety requirements in terms of a specification for maximum tolerable failure rates.[38] In 1961, the UK Air Registration Board (ARB) of the CAA issued a working document BCAR 367 "Airworthiness Requirements for Autoflare and Automatic Landing" which formed the basis for the definitions for weather visibility categories adopted by ICAO in 1965. In 1959, contracts were placed by BEA and BOAC to develop automatic landing, based on Autoland, for the Trident and the VC10.