Electronic Flight Information System (EFIS) — Page 287, Lesson 286

Let's start with the Electronic Flight Information System — EFIS. This is the system that puts all your navigation, weather, and traffic information onto one screen in the cockpit. The regulatory foundation here is EASA CS-25, specifically the advisory material AMJ 25-11. That's the document manufacturers must follow when designing the electronic horizontal situation indicator, the EHSI. It sets the colour coding rules, and it demands that there can be no confusion between colours or symbols. It also defines the probability that essential information — like attitude, altitude, or heading — will not be lost or displayed inaccurately. You don't need to memorise the full CS-25 spec for the exam; what you need is reproduced right here in this chapter. Now, the EHSI itself. It displays three kinds of information: navigational information, radar information, and TCAS information. For the Radio Navigation exam, what matters most is the navigational information — you need to know it and be able to interpret it. Let's trace the inputs. The EHSI receives data from the IRS — that's the Inertial Reference System. From the FMC, the Flight Management Computer. From VOR, DME, ILS, and ADF — the radio navigation aids. From TCAS, the Traffic Collision Avoidance System. And from AWR, which is the airborne weather radar. All of these feed into the port and starboard EHSI through their respective symbol generators. The symbol generators are the heart of the EFIS — they process all those inputs and generate the correct symbology for the display. The EHSI controller is your interface. It has a function switch to select the display mode, a range selection switch, and six switches to control what data is shown. Let's look at the display modes. There are four: Full VOR/ILS — sometimes called full rose — Expanded VOR/ILS, MAP, and PLAN. Now, weather radar and TCAS information can only be shown on the expanded VOR/ILS and MAP displays. The selectable map background options are enabled in the Map and Plan modes. What information can you display? The tuned VOR/ADF radials — that's the VOR/ADF option. Navigation Aids, labelled NAV AID. Airports, ARPT. Route Data, RTE DATA. Waypoints, WPT. And Weather, WXR. There's a traffic switch in the centre of the range selection knob. When you press it, one of three things happens: it displays TCAS information if it's not already shown, it removes TCAS information from the display, or — if TCAS FAIL is displayed — it removes that message. One important orientation point: with the exception of PLAN mode, which is orientated to true north, all the displays are orientated to aircraft heading, which may be either magnetic or true. And the range arcs — those are the white arcs showing distance — are displayed in the expanded VOR and ILS modes when the WXR switch is on, and in MAP mode at all times. Let me show you what this looks like on the actual display. That's the EFIS layout. And here's the map mode in detail. So to pull it together: the symbol generators take everything from the IRS, FMC, nav aids, TCAS, and weather radar, and turn it into a coherent picture. You select the mode with the function switch, pick your range, and use those six switches to layer on the data you need — VOR/ADF radials, nav aids, airports, route data, waypoints, or weather. And remember, weather and traffic only appear on expanded VOR/ILS and MAP, and PLAN is always true north while everything else follows your heading.