Safe expedition of air traffic

I PROPOSE to devote most of the article to air traffic control — the equipment involved, and the controllers, and that ‘in’ subject, the man‐machine interface. But first I intend to spend a little time on some other ground equipments, some navaids, which are much easier for an engineer to talk about because, so long as they keep on working, he can keep that awkward character, the man, out of the picture.