Flight Management System — Page 283, Lesson 335

We're starting a new chapter now — Chapter 22, the Electronic Flight Information System, or EFIS. But before we get into the displays themselves, I want to make sure you understand the annunciators on the Control Display Unit, the CDU, because those are the little warning lights that tell you what the Flight Management System is doing. There are four of them on the front of the CDU, and each one has a specific colour and a specific meaning. The first is MSG. It illuminates white. When you see it lit, it means there's an alerting or advisory message, or there are pending messages waiting for you. Think of it as the system tapping you on the shoulder — something needs your attention, either right now or shortly. The second is FAIL. This one is amber. If it's lit, it means an FMC failure has been detected — the Flight Management Computer itself has a problem. Amber is the caution colour, so this is telling you something is wrong with the core computing unit. The third is DISPLAY. It's also white. This one lights up when the page displayed is not related to the active flight plan leg or to the current operational performance mode. In other words, you're looking at a screen page that doesn't match what the aircraft is actually doing right now. It's a reminder that what you're viewing isn't the live, relevant data. The fourth is OFFSET. Again, white. This illuminates when a parallel offset is in use — that means the aeroplane is flying parallel to, but a fixed distance from, the FMS preprogrammed track. So instead of being right on the planned route, you're deliberately flying alongside it, and this light tells you that's happening. Now, those four annunciators — MSG, FAIL, DISPLAY, OFFSET — are your interface with the FMS. Remember them by colour and function: white for information, amber for failure. That brings us into the main topic of this chapter: the Electronic Flight Information System, the EFIS. This is the system that actually presents your flight data on the screens in front of you. Let me give you the structure of what we're going to cover, because it's a big system. We start with the units of a system — the physical components. Then we look at Symbol Generators, or SGs — these are the computers that generate the symbols you see on screen. Then the Display Units themselves — the actual screens. After that, the Colour Display System, which controls how information is coloured. Then the Remote Light Sensor, which adjusts display brightness. Then the Control Panel — that's your interface for selecting what you see. The control panel is split into two main sections. There's the 'EADI' section — that's the Electronic Attitude Director Indicator — and the 'EHSI' section — the Electronic Horizontal Situation Indicator. We'll cover the EADI display presentation, including Decision Height (DH) selection, and then the EHSI display presentation, which includes different modes like Full VOR, Expanded VOR, Full ILS, and Expanded ILS. Let me show you the overall layout. Here's Figure 22.1 — the multi-crew EFIS units and how they interface with signals. And here's the EFIS control panel itself, Figure 22.2. And Figure 22.3 shows a Boeing EADI where Decision Height is selected on the ADI control panel and displayed on both the ADI and elsewhere. So that's our roadmap. We've got the four CDU annunciators under our belt, and now we're moving into the EFIS — starting with the units of the system and the symbol generators. Let's dig into that next.