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

Let's begin with the Electronic Flight Information System — EFIS. This is the system that puts all your navigation, weather, and traffic information onto the displays in front of you. First, the regulatory foundation. The document EASA CS-25, specifically AMJ 25-11, is the advisory material manufacturers must follow when designing the electronic horizontal situation indicator — the EHSI. That's the display that shows you a horizontal view of your position relative to navigation aids, waypoints, and the like. AMJ 25-11 specifies the colour coding to be used on these displays, and it requires manufacturers to ensure there can be no confusion between colours or symbols. It also defines the probabilities that essential information — attitude, altitude, heading, and so on — will not be lost or inaccurately displayed. So it's about reliability and clarity of the most critical data. For the examination, you don't need detailed knowledge of the full CS-25 specification; what you need has been reproduced in this chapter. Now, the EHSI controller. The EHSI displays three types of information: navigational information, radar information, and TCAS information — that's the Traffic Collision Avoidance System. For the Radio Navigation examination, what's essential is your knowledge of, and ability to interpret, the navigational information. Let's look at the inputs to the EHSI. They come from five sources: the IRS — the Inertial Reference System; the FMC — the Flight Management Computer; the VOR, DME, ILS, and ADF navigation receivers; the TCAS; and the AWR — the Airborne Weather Radar. All of this information is fed to the port and starboard EHSI through their respective symbol generators. The symbol generators are the heart of the EFIS — they process the various inputs to generate the correct symbology for the EHSI. So the raw data comes in, the symbol generator turns it into the symbols you see on screen. The EHSI controller itself has a function switch to select the mode of the displays, a range selection switch, and six switches to control the display of data. Let me walk you through the display modes available. There are four: Full — or full rose — VOR/ILS; Expanded VOR/ILS; MAP; and PLAN. Now, an important limitation: weather radar and TCAS information can only be displayed on the expanded VOR/ILS and MAP displays. So if you're in Full VOR/ILS or PLAN mode, you won't see weather or traffic. The selectable map background options are enabled in the Map and Plan modes. The information available for display includes: tuned VOR/ADF radials — that's the VOR/ADF option; Navigation Aids — NAV AID; Airports — ARPT; Route Data — RTE DATA; Waypoints — WPT; and Weather — WXR. Each of these is controlled by one of those six switches. There's also a traffic switch in the centre of the range selection knob. When you press it, it does one of three things: it displays TCAS information if it's not already displayed; it removes TCAS information from the display if it is displayed; and when TCAS FAIL is displayed, pressing it removes that message. One more critical point about orientation. With the exception of the PLAN mode, which is orientated to true north, all the displays are orientated to aircraft heading — and that heading may be either magnetic or true. So in PLAN mode, north is always up; in the other modes, the display is aligned with where the aircraft nose is pointing. Finally, the range arcs — those are the white arcs showing distance rings. They're displayed in the expanded VOR and ILS modes when the WXR switch is on, and in the MAP mode at all times. So in MAP mode you always see those white range arcs; in expanded VOR/ILS you only see them when weather radar is switched on. That's the core of the EFIS introduction — the regulatory basis, the inputs, the symbol generators, the controller, the display modes, and the orientation rules.