Future Air Navigation Systems (FANS) — Page 322, Lesson 376

I want to walk you through the opening of the Future Air Navigation Systems chapter, because this is where we set up the entire problem that FANS is designed to solve. So let's start with the big picture. Right now, today, aircraft are controlled using voice communications. That's the baseline. Over and close to populated landmasses, air traffic control uses radar to provide positive control of aircraft, and they talk to the pilots using VHF communications. VHF is very high frequency radio, and radar gives ATC a direct, continuous picture of where every aircraft is. But here's the catch. Over oceans, deserts, and polar regions, VHF and radar may not be available. There's no radar coverage out there, and VHF doesn't reach that far. So ATC has to fall back on something called a procedural control service. That generally requires HF communications — high frequency radio, which is the long-range voice link. And the consequence of procedural control is significant: it results in high vertical, lateral, and longitudinal separation distances. In plain terms, aircraft have to be spaced far apart in all three dimensions, which means the airspace can only carry a low traffic density. Fewer aircraft per hour can cross those regions safely. Now let me make that concrete with the North Atlantic. Position reports are passed by aircraft crossing the North Atlantic every 10° of longitude up to 70°N, and every 20° north of that. So as you fly west across the ocean, you call in your position at each of those longitude lines. The result is that ATC receives a position update only every 30 to 60 minutes. Think about that — the controller's picture of where you are is up to an hour old. That's why the separation distances have to be so large. And it gets worse. With the increase in international air traffic, this is posing major limitations. And those limitations are compounded by the difficulties associated with HF communications. Here's the key operational point: in these remote areas, the pilot is rarely communicating directly with the ATC controller. Instead, the pilot talks through a third party who relays messages between the two. So you have a human relay in the middle, which adds delay and the risk of error. Now contrast that with the populated areas. Over and around populated areas, radar allows positive identification and control of aircraft. The controller sees you, knows exactly who you are, and can give you tight, efficient clearances. So the need is clear. To increase capacity over the rest of the world — over those oceans, deserts, and polar regions — ATC needs real-time information on aircraft positions. And that position information must have improved accuracy. Plus, we need better communications between the air traffic controller and the pilot. Those are the two pillars: accurate, real-time position data, and reliable direct communication. And here's where technology has caught up. We now have global satellite navigation systems — GNSS — providing position accuracy to better than one nautical mile. One NM. That's a huge improvement over the old procedural estimates. Now, I'll be honest with you, there are still some issues with the service provided by GNSS, but in general, this high level of position accuracy is now globally achievable. And we also have satellite communication systems — SATCOM — which give us the potential for global communications. So that's the foundation. Voice and radar work well over land, but fail over remote areas. Procedural control with HF and relayed messages forces huge separations and low capacity. GNSS gives us the accurate positions, and SATCOM gives us the global link. FANS is about putting those pieces together. Let's keep going.