Thiry-three years ago, by an ironic fate, a man passionately concerned with safety in air travel, which he hoped to achieve by a radical change from fixed to rotating wings, lost his life in an aeroplane accident. Since de la Cierva's tragic death, civil air transport has grown to a spectacular system, especially if one considers the speed of modern aircraft and the size of modern airports. It is, however, still quite small by comparison with other mass transport systems, if one takes ton-mileage or passenger-mileage as the yard-stick. Indeed the penetration of the aircraft into road, rail and sea traffic has not been very impressive except across the Atlantic and perhaps on certain routes in the USA. The modern airliner with a casualty probability of the order of 10-6 per passenger flight is considered a fairly safe means of transport. Although the cost of air travel is comparatively high, the mode of travel, especially the high cruise speed, is attractive.