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 display units themselves, I want to close out the Flight Management System chapter with the illuminated annunciators on the front of the CDU — the Control Display Unit. These are the little lights that tell you what the system is doing, and you need to know exactly what each one means. There are four annunciators. Let's take them one by one. First is MSG. It illuminates white. It indicates an alerting or advisory message, or that there are pending messages. So if you see MSG lit, the FMC is trying to tell you something — either a message is waiting for you, or there's an alert you need to acknowledge. Second is FAIL. This one illuminates amber. It lights if an FMC failure is detected. Amber is your warning colour — this is the one you really pay attention to, because it means the Flight Management Computer itself has failed. Third is DISPLAY. It also illuminates white. It lights if the page you're currently displaying is not related to the active flight plan leg, or not related to the current operational performance mode. In other words, the screen is showing you something that doesn't match what the aircraft is actually doing right now. It's a reminder that you're looking at the wrong page. Fourth is OFFSET. Again, white. It illuminates when a parallel offset is in use — that is, when the aeroplane is flying parallel to, but a fixed distance from, the FMS preprogrammed track. So if you've offset your path to avoid weather or traffic, OFFSET tells you that you're not on the programmed track itself, but alongside it. So to summarise the colours: MSG, DISPLAY, and OFFSET are all white — they're informational. FAIL is amber — it's a warning. That's your quick mental check. Now, that closes out the FMS chapter. We're moving into Chapter 22, the Electronic Flight Information System. This is the system that actually presents all that flight data to you on the screens. Let me give you the structure of what we're covering. We start with the EFIS itself, then the units of the system — the Symbol Generators, the Display Units, the Colour Display System, the Remote Light Sensor, and the Control Panel. Then we get into the two main displays: the EADI and the EHSI. We'll cover the EADI section of the control panel, the EADI display presentation, and Decision Height — DH. Then the EHSI section, system symbols, and the EHSI display presentation in its various modes: Full VOR, Expanded VOR, Full ILS, and Expanded ILS. Let's begin with the big picture. The EFIS — Electronic Flight Instrument System — is what replaces the old electromechanical instruments. Instead of separate spinning gyros and needles, you get electronic displays driven by computers. The whole system is built from several key units, and I want you to understand how they fit together. First, the Symbol Generators — the SGs. These are the computers that generate the symbols you see on the screens. They take raw data from the aircraft's sensors and turn it into the graphical symbology — the attitude indicator, the heading, the course line, all of it. Think of them as the brains that draw the picture. Then the Display Units — these are the actual screens, the EADI and EHSI, that show you the picture the symbol generators create. The Colour Display System is what gives you the colour coding — the greens, ambers, reds, whites — that make the displays readable at a glance. The Remote Light Sensor adjusts the display brightness automatically based on the ambient light in the cockpit. Bright sunlight, it brightens the screen; night, it dims it. And the Control Panel is where you, the pilot, select what you want to see and how you want to see it. Let me show you the signal flow. That figure shows the multi-crew EFIS units and how they interface — how the symbol generators talk to the display units and the control panels. You can see the redundancy built in for a two-pilot cockpit. Now, the control panel itself. This is where you make your selections. It's divided into two sections: the EADI section and the EHSI section. Let's start with the EADI. The EADI — Electronic Attitude Director Indicator — is the primary flight display. It shows you the attitude of the aircraft, the pitch and roll, plus the flight director commands. On the control panel's EADI section, you have your selection knobs and switches for things like the decision height. And that brings us to Decision Height — DH. This is a critical concept for approaches. Decision Height is the altitude at which you must decide whether to continue the approach or execute a missed approach. On the EADI, you set the DH value on the ADI control panel, and it's shown on both the ADI and on the display itself. That figure shows a Boeing EADI with the DH selected. When you descend to that height, you get the visual and aural alert, and you make your decision. Now, the EHSI — Electronic Horizontal Situation Indicator. This is the navigation display. It shows you your position relative to the ground, the course, the VOR or ILS radials, the heading. On the control panel's EHSI section, you select the mode — and that's where the different presentations come in. You have Full VOR mode — the full compass rose with the VOR information. Expanded VOR — a magnified view, where the compass rose is expanded so you see more detail in the direction of flight. Full ILS mode — the full compass rose with ILS localizer and glideslope information. And Expanded ILS — the expanded view with the ILS data. And there are system symbols — the little icons on the display that tell you about the state of the system, like which navigation source is active. So that's the roadmap. We've got the units, the control panel, the EADI with its DH, and the EHSI with its modes. Let's go through them in detail, starting with the units of the system.