Observer's book of aircraft ; 1957 Observer's book of aircraft ; 1958 Observer's book of aircraft ; 1959 Observer's book of aircraft ; 1960 Observer's world aircraft directory ; 1961 Observer's book of aircraft ; 1962 Observer's book of aircraft ; 1963 Observer's book of aircraft ; 1964 Observer's book of aircraft ; 1965 Observer's book of aircraft ; 1966 Observer's book of aircraft ; 1967 Observer's book of aircraft ; 1968