Area Navigation Systems (RNAV) — Page 262, Lesson 260

Let’s start with the big idea. A simple RNAV system, which stands for Area Navigation, lets you fly a route that isn’t tied to flying directly to or from a ground station. Instead of chasing a VOR radial, you define points in space — waypoints — and the system navigates you to them. The heart of a simple 2D RNAV system is what we call rho/theta, which is just range and bearing. Rho is the Greek letter for range, theta for bearing. So the system defines your position using a range and a bearing from a VOR/DME station. The VOR gives you the bearing, the DME gives you the range, and together they fix your position. Now, here’s how you use it. You, the pilot, define waypoints along your route, and you define each one as a range and bearing from a suitably located VOR/DME. Suitably located means the station is close enough and positioned so the geometry is good. Then the equipment takes the VOR/DME bearing and range, and it computes two things for you: the QDM and the distance to the waypoint. QDM is the magnetic bearing you’d fly to reach that waypoint. And it presents this information to you on a CDI — that’s a Course Deviation Indicator — or on an HSI, a Horizontal Situation Indicator. The key trick is that it presents it as if the waypoint itself were a VOR/DME station. That’s why these waypoints are called phantom stations. They don’t exist as physical ground equipment; they’re just computed points that behave like one for your instruments. Let me give you a concrete example from the route diagram. The pilot has defined waypoints along a planned route from SND to NEW, using available and sensibly placed VOR/DME stations. Look at the waypoint definitions: 066R/29 NM, 218R/26 NM, 067R/42 NM. Each one is a bearing and a range from a chosen station. 066R means radial 066, 29 NM means 29 nautical miles out. So each waypoint is locked to a specific VOR/DME by that radial and distance. Now, what can you use these waypoints for? Four things. First, en route navigation — just flying your planned route. Second, initial approach fixes — the points where an approach procedure begins. Third, Locator Outer Markers — those are the markers on an ILS approach. And fourth, ILS frequencies. Here’s the interesting part: when you select an ILS frequency as a waypoint, the instrumentation automatically reverts to ILS mode. So the system hands control back to the ILS receivers. So the whole philosophy of a simple 2D RNAV system is this: you’re not flying to the station, you’re flying to a phantom station you defined, and the system does the trigonometry to make your CDI or HSI behave as if that phantom station were real. That’s the core of it.