It is not possible to go fully into all the aspects of this problem in the time at my disposal. I am accordingly confining myself to a discussion of the feasibility of operating heavier-than-air craft in fog with reference to the instrumental equipment required. The meteorological aspects were dealt with in a paper by Captain Entwistle two years ago.

In order to obtain a correct perspective on the problems of flying in fog it is necessary to realise that many cases of impaired visibility, which would not normally be regarded as fogs, may seriously increase the risks of flying. This reduction of visibility may be caused by fog proper or by haze, drizzle, rain, snow or dust. The problem I wish to consider then is that of flying, navigating and landing when the visibility is such, that flight would be impossible or unduly dangerous without special equipment.