HC Deb 16 November 1938 vol 341 c866
55. Mr. Simmonds

asked the Secretary of State for Air what provision he has made to prevent trials with the balloon barrage from being a danger to aircraft in conditions of bad visibility?

The Secretary of State for Air (Sir Kingsley Wood)

The instructions are that balloons should not be flown in conditions of bad visibility, that is when the horizontal visibility from an aircraft is less than 1,100 yards, or at night when aircraft lights cannot be seen at that distance.