Control of Aircraft — Page 326, Lesson 428

I want to walk you through the origins of procedural air traffic control, because this is where the whole idea of ATC as we know it was born. And it's a story that starts with a very grim statistic. The provision of ATC to air traffic is largely a post-World War II concept. Before that, there really wasn't a systematic service. The need for it was highlighted by the high loss rate of aeroplanes during WW2, on and in the vicinity of aerodromes. And the causes were specific: mid-air collisions, collisions with obstacles, and inadvertent flight into terrain. So the first response was to establish ATC at aerodromes, provided by the control tower. But here's the key limitation — beyond the aerodrome boundary, which is now replaced by the ATZ, the Aerodrome Traffic Zone, little was provided other than a 'flight following' monitoring service. And that service was essentially just to ascertain that the aircraft was still airborne. That's it. No separation, just confirmation that you hadn't crashed. Now, the catalyst for change came after an accident in the US involving two Constellations over the Grand Canyon in the early 1950s. Two Lockheed Constellations collided in mid-air. And the concern that was expressed was this: two relatively small objects flying over a vast geographic area could be a threat to each other. That seems obvious now, but at the time it was a revelation. This led to the establishment of a 'one-way' system for east/west flight over the continental US. And that gave rise to the first established 'procedural' ATC service. So let me define what procedural ATC actually is, because that's the core of this excerpt. The service provided separation by requiring aircraft naturally cruising at the same altitude to fly via different routes. That's lateral geographic separation. So instead of relying on radar to see where planes are, you separate them by geography — different routes at the same altitude. It required the pilot to tell the air traffic controller where the aircraft was by passing position reports. So the pilot is the sensor. The data collected was plotted, and as the flight progressed, any apparent collision risk was determined, and the flights concerned would be asked to alter course to eliminate the problem. Now, the problems with this system were significant, and I want you to remember these because they explain why we later moved to radar. The equipment used to determine the aircraft position was, by modern standards, somewhat crude. The communications equipment and facilities were poor. And the availability of flight information, including met data — meteorological data, weather — was virtually nonexistent. However — and this is the crucial qualifier — the density of air traffic was also low. That's the saving grace. The system worked only because there simply weren't that many aircraft in the sky. So the takeaway here is the fundamental principle of procedural control: separation is achieved by design, by route planning and pilot position reports, not by real-time surveillance. The pilot tells the controller where he is, the controller plots it, and if two flights look like they'll conflict, the controller asks one to change course. It's slow, it's crude, and it depends entirely on the accuracy of the pilot's report and the quality of the communications. But it was the first real ATC service, and it set the template for everything that followed.