ElectronicFlightInformationSystems — Page 55, Lesson 47

I want to walk you through the failure annunciation and symbol colour conventions used on Electronic Flight Information Systems — EFIS — in a modern cockpit. Let’s start with failure annunciation. When a data signal fails — for example, from the Instrument Landing System, the ILS, or from the radio altimeter — that failure is displayed on each screen. So if the ILS signal drops out, or the radio altimeter stops sending valid height data, you will see that failure indicated right on the display. In addition to those signal-failure flags, fault messages may also appear. For instance, if the associated Flight Management Computer and the weather radar range disagree with the range data set on the control panel, a fault message will be displayed. So the system is constantly comparing what the control panel says the range should be against what the FMC and weather radar are actually using — if they don’t match, you get a fault message. Now let’s move to the Navigation Displays. The symbols you see on each Horizontal Situation Indicator — the HSI — depend on what the EFIS Control Panel switch is set to. Different switch selections bring up different symbols. Those symbols are displayed in different colours, and the general colour presentation follows a standard convention. Let me run through each colour and what it means. Green — abbreviated G — is used for engaged flight mode displays and dynamic conditions. So if a mode is actively engaged and controlling the aircraft, or if a value is changing dynamically, it shows in green. White — W — shows the present status or situation, scales, and armed flight mode displays. So things that are set and ready but not yet active, or fixed scales and current data, appear in white. Magenta — M, sometimes called pink — is used for command information, pointers, symbols, and the fly-to condition. So if the system is telling you where to steer or what target to fly to, that guidance appears in magenta. Cyan — C, which is blue — shows non-active and background information. Things that are present on the display but not currently in use or not the primary focus. Red — R — is for warnings. A red indication means something that requires immediate attention. Amber — A — is for cautionary information, faults, and flags. So less urgent than a red warning, but still something you need to be aware of. Black — B — is for blank areas or when a display is turned off. Now let’s look at the specific symbols that can appear on the HSI, depending on the mode selected. First, the Distance Display. In PLAN or MAP mode, or when tuned to a VOR or ILS, you can see a distance readout. It shows the distance to the next FMC waypoint in nautical miles, or the distance from a tuned VOR or ILS navaid via DME. The display might show something like 200 NM or 4.4 NM, or it might show DME 124 or DME 24.6. Next, the Heading indicator. In PLAN, MAP, VOR, or ILS mode, you see a heading readout. The number under the pointer is a heading, and if there is a box around it, that indicates the actual heading. The heading is referenced to magnetic north between 60 degrees South and 73 degrees North latitude, if that magnetic reference is selected. Above those latitudes, the heading reference switches to true north. Then we have the ETA Display — estimated time of arrival. In PLAN or MAP mode, it shows the ETA at the active waypoint, based on current ground speed. The colour can be magenta or white. Next is the Selected Heading Marker. In PLAN, MAP, VOR, or ILS mode, this indicates the heading that has been set in the Mode Control Panel — the MCP. A dotted line in magenta extends from the marker to the aeroplane symbol. That dotted line makes it easier for you to track the heading marker when it is out of view — except in plan mode, where that line is not drawn. Then we have the Expanded Compass Rose. In PLAN, MAP, VOR, or ILS mode, the compass data is provided by the selected Inertial Reference System — the IRS. The full 360 degrees of heading are available, but typically only about 70 degrees of the compass rose is displayed at a time. Finally, the Full Compass Rose. This is used in Full VOR or Full ILS mode. The compass data is again provided by the selected IRS. That covers the failure annunciation, the colour conventions, and the key symbols you will see on the EFIS navigation displays.