Electronic Flight Information System (EFIS) — Page 298, Lesson 295

I want to walk you through the EFIS map display — the Electronic Flight Information System — and specifically what you're seeing on that navigation display when you're in MAP or PLAN mode. This is the page that tells you exactly what each symbol, colour, and line on your screen means, and as a professional pilot you need to know these cold. Let's start with the runway symbol. It's available when the EHSI display range is 10, 20, or 40 nautical miles. EHSI stands for Electronic Horizontal Situation Indicator — that's the map portion of your EFIS. The runway is displayed if the airport has been selected as the origin or destination airport, with a specific runway selected. So it's not just any airport — it's your departure or arrival field, and you've picked a particular runway. The runway symbol is scaled to represent the length of the selected runway, so a longer runway draws longer on the screen. And here's a precise number for you: the dashed centre lines extend outward 14.2 nautical miles from the runway thresholds. That's the extended centreline you see leading away from each end of the runway. Next, the vertical profile points. These are shown in green, and they represent an FMC-computed vertical profile point in the active flight plan. FMC is the Flight Management Computer. The identifiers are T/C for top-of-climb, T/D for top-of-descent, S/C for step-climb, and E/D for end-of-descent. So when you see T/C on the map, that's where you'll reach your cruise altitude; T/D is where you begin your descent; S/C is a step-climb point; E/D is the end of descent. One important detail: a deceleration segment point has no identifier — it's just a symbol without a letter label. Now let's talk about navaids — navigation aids. There's a NAV AID switch on your EFIS control panel. When it's OFF, tuned navaids, excluding NDBs — that's Non-Directional Beacons — are displayed in green. So only the ones you've actually tuned in, and no NDBs. When the NAV AID switch is ON, all appropriate navaids in the FMC database and within the MAP area are displayed when the range is 10, 20, or 40 NM. But here's the altitude distinction: only high altitude navaids are displayed when the selected range is 80, 160, or 320 NM. So at the longer ranges, you only see the high-altitude aids. Navaids not being used are displayed in cyan — that's the blue colour. Now, VOR radials. When a VOR navaid is manually tuned, the associated MCP selected course and its reciprocal are displayed. MCP is the Mode Control Panel — that's where you set your selected course. So you'll see the course you've dialled in, plus the opposite radial, 180 degrees away. But there's a condition: the VOR/ADF switch on the EFIS control panel must be ON, and a valid VOR signal must be received. No valid signal, no radial display. Let me also clarify the colour coding you'll see in the legend. The airport and runway symbol is white — that's the W. Vertical profile points are green — G. Identifiers are green. VOR is shown in cyan or green — C, G. DME/TACAN is cyan or green. VORTAC is cyan or green. Manually tuned VOR radials are green, and VOR radials are green. So cyan means the navaid is in the database but not being used; green means it's active or tuned. Now, ADF bearings. ADF is the Automatic Direction Finder. These are displayed in green, and again the VOR/ADF switch on the EFIS control panel must be ON, and a valid ADF signal must be received. When those conditions are met, the display shows the relative bearing to the tuned ADF station or stations. Relative bearing means the angle measured clockwise from the nose of the aircraft to the station. Next, the selected fix. This is depicted as a fix symbol and identifier, in cyan or green, and it appears in both MAP and PLAN modes. It depicts the selected reference point as entered on the FMC/CDU FIX INFO page. CDU is the Control Display Unit — that's your FMC interface. This fix can appear with other special map symbols, like a VOR, VORTAC, airport, or waypoint, if that fix is stored in the FMC database. So you're placing a reference point on your map. Around that fix, you get a selected fix radial and a selected fix circle, both in green. A fix reference radial is displayed for each downtrack bearing you enter on the FMC/CDU FIX INFO page. So if you enter a bearing, you see a line radiating from the fix. And a DME reference circle is displayed for each distance you enter on that same FIX INFO page. DME is Distance Measuring Equipment — so each distance you enter draws a circle at that range around the fix. Finally, the holding pattern. It has three colour states: active is magenta — that's the M; modification is white — W; inactive is cyan — C. It appears in both MAP and PLAN modes. Here's the scaling rule: it appears as a fixed size holding pattern if the selected range is greater than 80 NM. So at long range, it's just a standard-size symbol. But a scaled representation of the holding pattern is displayed when the selected range is 80 NM or less, and the aeroplane is within 3 minutes of the holding fix. So when you're close and at a short range, the pattern is drawn to true scale so you can see exactly where to fly. That's the full map display legend. Every symbol, every colour, every range limit — the 14.2 NM centreline, the 10/20/40 versus 80/160/320 navaid ranges, the 80 NM holding pattern break, the 3-minute rule. These are the details that make the difference between reading a map and flying a professional instrument approach.