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

Let’s start with the Electronic Flight Information System, or EFIS, and I want to walk you through the map display symbols and their rules. This is the part of the system that draws the navigation picture on your EHSI — the Electronic Horizontal Situation Indicator — and every symbol you see has a specific condition attached to it. First, the airport and runway symbol, shown in white. It’s available only when the EHSI display range is 10, 20, or 40 nautical miles. It’s displayed if the airport has been selected as the origin or destination airport, and only when a specific runway has been selected. The runway symbol is scaled to represent the length of that selected runway. And here’s a precise number: the dashed centre lines extend outward 14.2 nautical miles from the runway thresholds. So that’s not a guess — it’s a fixed 14.2 NM extension beyond each threshold. Next, vertical profile points, shown in green. These represent an FMC-computed vertical profile point in the active flight plan. 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. A deceleration segment point has no identifier — it’s just drawn without a label. Now the navaids. There’s a NAV AID switch on the EFIS control panel. When it’s OFF, only tuned navaids — excluding NDBs — are displayed, and they appear in green. When the NAV AID switch is ON, all appropriate navaids in the FMC database and within the MAP area are displayed, but only when the range is 10, 20, or 40 NM. If the selected range is 80, 160, or 320 NM, only high-altitude navaids are displayed. Navaids not being used are shown in cyan, which is a blue colour. Now the VOR radials. When a VOR navaid is manually tuned, the associated MCP selected course and its reciprocal are displayed. But there are two conditions: the VOR/ADF switch on the EFIS control panel must be ON, and a valid VOR signal must be received. So no valid signal, no radial display. Similarly, ADF bearings are shown in green. The same switch condition applies — the VOR/ADF switch 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. Now the selected fix. This is depicted as a fix symbol and identifier, in cyan or green, and it appears in MAP and PLAN modes. It depicts the selected reference point as entered on the FMC/CDU FIX INFO page. It can appear with other special map symbols — like a VOR, VORTAC, airport, or waypoint — if that fix is stored in the FMC database. Then we have the selected fix radial and the selected fix circle, both in green, again in MAP and PLAN. A fix reference radial is displayed for each downtrack bearing entered on the FMC/CDU FIX INFO page. And a DME reference circle is displayed for each distance entered on that same FIX INFO page. So the radial comes from a bearing you entered, and the circle comes from a distance you entered. Finally, the holding pattern. It can be active, shown in magenta; a modification, shown in white; or inactive, shown in cyan. It appears as a fixed-size holding pattern if the selected range is greater than 80 NM. But when the selected range is 80 NM or less, and the aeroplane is within 3 minutes of the holding fix, a scaled representation of the holding pattern is displayed. So the rule changes with range and proximity. That’s the full map symbol set for this part of the EFIS. Every symbol has a mode condition — MAP or MAP/PLAN — and a colour code, and the navaid and bearing displays depend on switch positions and valid signals.