BLIND FLYING first became important when the snail-mails started being entrusted to aeroplane. Before that, pilots would either land if visibility deteriorated, or, alternatively, descend very low over the nearest town to check out the sign on the railway station, after which they would (a) re-plot their course or (b) crash onto the tracks, wiping out a trainload of innocent children on their way to the school treat for which they had saved their precious pennies for months and months and months. (This was known as 'Pilotage' or 'Carnage' according to which side you were on.)

With mail-flying, though, came the need for flying in all weathers. Aircraft could stay upright thanks to artificial horizons and other instruments, but navigation was harder. The American mail planes flew across the continent, in the early days, by following lines of bonfires whose light shone (such was the theory) through even the densest cloud: precursors of our modern system of radio beacons. Like so much of aviation, the metaphor was that of marine navigation, and it's interesting to note that even modern, highly-equipped airports still have a sort of lighthouse on the roof, flashing an individual pattern of lights instantly recognised by all pilots as 'What the hell is that flashing light over there?'