Selects range for displayed navigation data and WXR — Page 289, Lesson 346

I want to walk you through the EFIS control panel and the EHSI display presentation. We're going to look at how the crew selects what navigation data appears on the screen, and then how that data is actually presented to you. Let's start with the control panel. The first function is the MODE SELECTOR. This is the rotary switch that selects the display appropriate to the mode you need. You have four choices: VOR, ILS, MAP, and PLAN. Each one calls up a different presentation on the EHSI. Next to it is the BRT, or BRIGHTNESS control. Notice it's actually two concentric knobs. The outer knob sets the main display brightness — that's the overall brightness of the EHSI screen. The inner knob sets the WXR display brightness — that's the weather radar overlay brightness, separate from the main picture. Then we have the MAP switches. These are only used in MAP mode. When you select one of these switches, it causes its placarded data to be displayed on the EHSI. The placards are: NAV AID, which stands for NAVIGATION AID; ARPT, which is AIRPORT; RTE DATA, which is ROUTE DATA; and WPT, which is WAYPOINTS. So in MAP mode, you push these to toggle that specific category of data on or off the display. There's also the EXP ARC switch. This selects VOR or ILS mode to show an Expanded Arc. I'll explain what that means in a moment when we get to the display modes. Finally, the WXR switch. When pushed in, WXR data is displayed during all modes except PLAN, or when the VOR / ILS mode is selected to present the FULL compass rose. So weather radar is available in most modes, but not in PLAN, and not when you've chosen the full compass rose presentation of VOR or ILS. Now, before we get into the display itself, I want to cover the System Symbols — these are the colours you'll see on the EHSI, and each colour has a specific meaning. The Active Waypoint is shown in Magenta — that's the waypoint the aircraft is currently navigating to. The Inactive Waypoint is shown in White — that's a navigation point making up the selected active route, but one you're not currently flying to. Airports are shown in Cyan. An Off Route Waypoint is also Cyan. Tuned Navaids are shown in Green — these are the navaids you've actually selected and tuned. An Unused Navaid is shown in Cyan. And finally, Wind Direction is shown in White, with respect to the map display orientation and compass reference. The symbol is shown in white against the black of the screen. Now let's move to the EHSI Display Presentation. The EHSI presents a selectable, dynamic colour display of flight progress and a plan view orientation. There are four principal display modes you can select on the EFIS control panel: VOR, ILS, MAP, and PLAN. Of these, VOR and ILS can be displayed as full or expanded compass displays. And the orientation of the displays may be Magnetic or True, and Track or Heading, as selected. Let me walk you through the Full VOR Mode in detail, because it's the richest example. With a VOR frequency selected, the EHSI displays a full compass rose with the VOR source in the lower left and the frequency in the lower right. The course selection is displayed by the magenta course needle, with the tip pointing to the selected course — in the example, that's 150 degrees. Course deviation is shown by the traditional deviation bar moving across a two dot left and two dot right scale. So you have a scale of two dots each side of centre, and the bar shows how far off the selected course you are. A TO / FROM pointer is shown in addition to the TO / FROM annunciation — so you get both the pointer and the text indication of whether you're flying to or from the station. DME distance is displayed in the top left corner. The current heading is shown in the window and by the lubber line at the top of the compass rose — in the example, that's 130 degrees. The current selection is Magnetic Heading, as shown either side of the window. The current track is shown by the white triangle on the inside edge of the compass rose. The selected heading is shown by the magenta heading "bug" on the outer scale of the compass rose. Wind speed and direction are shown in the lower left corner, orientated to the display selection — that means it's orientated to Heading or Track, Magnetic or True, whichever you've selected. And one important limitation: Weather radar displays are not available in Full VOR mode. That ties back to the WXR switch — remember, WXR data is not shown when VOR/ILS is selected to present the full compass rose. So the key contrast here is between the full compass rose and the expanded arc. The full rose gives you the complete 360-degree picture, but no weather radar. The expanded arc, selected by the EXP ARC switch, gives you a partial arc of the compass — and that's where weather radar data can be overlaid. Let me show you the control panel and the display layout so you can see how all these controls and symbols fit together. That's the full picture of the control panel and the EHSI presentation. You've got the mode selector giving you VOR, ILS, MAP, and PLAN; the brightness knobs separating main and WXR; the MAP switches for NAV AID, ARPT, RTE DATA, and WPT; the EXP ARC for the expanded presentation; and the WXR switch with its limitation in PLAN and full-rose modes. And on the display itself, every colour and symbol has a precise meaning — magenta for active, white for inactive, cyan for airports and off-route points, green for tuned navaids.