We begin with an introduction, then we go straight into the EHSI Controller — Page 287, Lesson 285

We're starting a brand-new chapter today, and it's a big one: the Electronic Flight Information System, which we call EFIS for short. This is the system that puts all your flight and navigation data onto those glass screens in front of you, replacing the old mechanical instruments. Let me walk you through how this chapter is laid out, because it's structured like a proper build-up. We begin with an introduction, then we go straight into the EHSI Controller. Now, EHSI stands for Electronic Horizontal Situation Indicator — that's the screen that shows you your position relative to the ground, the navigation aids, and your course. The controller is the panel unit you use to select what that screen displays. From there, we move into the Display Modes — the different ways you can configure that EHSI screen. And there are several, and each one has a specific job. We have the Expanded VOR Mode, then the Full Rose VOR Mode. VOR, of course, is VHF Omnidirectional Range — the ground-based radio beacon that tells you your bearing to or from the station. The "expanded" version gives you a magnified, detailed view of the navigation information, while the "full rose" shows you the complete 360-degree compass rose with the VOR data overlaid on it. Then we have the Expanded ILS Mode and the Full Rose ILS Mode. ILS is the Instrument Landing System — the precision approach aid that gives you both lateral and vertical guidance down to the runway. Again, you have the choice between the expanded, detailed view and the full compass rose view. After those, we get to the Map Mode, which is exactly what it sounds like — a moving map display showing your aircraft's position relative to waypoints, airports, and airspace. And then there's the Plan Mode, which is used for route planning and review, typically with the aircraft symbol not moving, so you can study the whole route ahead. Once we've covered all the modes, the chapter moves into two critical sections: EHSI Colour Coding and EHSI Symbology. Colour coding is the standardised use of colours on the screen — for example, what's shown in green versus white versus magenta — and symbology is the meaning of every symbol and icon you'll see. These are absolutely essential, because in the cockpit you don't have time to think about what a symbol means; you have to know it instantly. Finally, the chapter ends with a set of Questions, followed by Appendix A and the Answers. So that's the roadmap for this chapter. Now, let's get into the heart of it. The whole point of EFIS is to integrate all your flight information into a single, coherent display. The EHSI is the horizontal situation indicator — it's your bird's-eye view of where you are and where you're going. The controller is the interface that lets you choose which mode you want to see. And each mode — Expanded VOR, Full Rose VOR, Expanded ILS, Full Rose ILS, Map, and Plan — is a different tool for a different phase of flight. Let me show you what the Map Mode actually looks like on the screen. That's the map mode in action. And here's the broader EFIS layout, showing how the whole system fits together on the instrument panel. So, as we go through this chapter, I want you to think of the EHSI as your primary navigation picture. The controller is how you tailor that picture to the task at hand — whether you're en route, on an approach, or planning ahead. And the colour coding and symbology are the language that picture speaks. Master that language, and you'll read the screen like a native speaker. Let's start with the controller and the display modes in detail.