Introduction — Page 1, Lesson 7

Let’s start at the very beginning of your radio navigation syllabus. I want to walk you through why this subject exists at all, because it frames everything else we’ll do. Radio and radar systems are now an integral and essential part of aviation. Without them, the current intensity of air transport operations would be unsustainable. Think about that for a moment. In the early days of aviation, aircraft were flown with visual reference to the ground. Flight at night, in cloud, or over the sea was simply not possible, because you had nothing to navigate by. As aircraft became more complex, it became necessary to design navigational systems that let an aircraft operate without any reference to terrain features. The early systems that were developed were, by modern standards, very basic and inaccurate. They gave reasonable navigational accuracy for en route flight over land, but only a very limited service over the oceans. And here’s a striking fact: until about 40 years ago, flight over the oceans used the traditional seafarer’s technique of astro-navigation. That means using sights taken on the sun, the moon, the stars, and the planets to determine your position. So the earliest ocean crossings were done the same way a ship would have done it centuries before. Development really commenced in the 1910s, continued at an increasing rate through the 1930s and 1940s, and right up to the present day. That led to long-range systems which, by the 1970s, were providing a global navigation service. Now here’s the irony I want you to hold onto. Having forsaken navigation by the stars, the most widely used navigation systems in the last few years are once again space based. That is, the satellite navigation systems we now take as being the norm. Global satellite navigation systems — GNSS — are becoming the standard in aviation, and many people advocate that they will replace totally all the terrestrial systems. But the ICAO view is different. ICAO — the International Civil Aviation Organization — takes the position that certain terrestrial systems will have to be retained to back up GNSS, both for en route navigation and for runway approaches. So you must understand: GNSS is not the whole story. Terrestrial systems stay in the picture as a backup. And finally, the development of radar in the 1930s allowed air traffic — and that sentence is cut off in our excerpt, but it sets the stage for the rest of the chapter, where we’ll get into the actual physics of radio waves. So the big picture for this introduction: radio navigation exists because visual reference isn’t enough, it evolved from astro-navigation to terrestrial systems to space-based GNSS, and ICAO insists we keep terrestrial backups. That’s the foundation. Next we’ll move into the properties of the radio waves themselves.