First, let's set the scene on range — Page 297, Lesson 352

Right, let's pick this up with the MAP display on the Electronic Flight Information System. This is the mode you'll use as your primary navigation picture in normal operations. First, let's set the scene on range. The range of the display is selected on the control panel. Now, here's a key detail: the display shows the half-scale range. So if you see "10 NM" displayed, that means the display is actually selected to 20 NM. The outer arc of the compass rose represents the furthest range from the aircraft — that's your 20 NM edge in this example. Now, the MAP mode itself. This is the mode used normally. It works in conjunction with the flight plan data programmed into the flight management computer — the FMC. The display shows information against a moving map background, and critically, all elements are drawn to a common scale. That means the map, the route, and the symbols all share the same scale, so distances are true. Let's look at the layout. The symbol representing the aircraft sits at the lower part of the display. At the upper part, you have an arc of the compass scale — the compass rose — covering 45 degrees on either side of the instantaneous track. So that's a 90-degree arc total, centred on where you're heading right now. Now, heading information. This is supplied by the appropriate inertial reference system. The compass rose is automatically referenced to magnetic north when you're between latitudes 73°N and 65°S. That's the normal case. But when you're above those latitudes — north of 73°N or south of 65°S — it automatically switches to true north. There's also a crew-operated MAG/TRUE selector switch. If you set that switch to TRUE, the compass rose is referenced to true north regardless of latitude. So the automatic switching is overridden by your manual selection. Now the route display. The aircraft's active route, as derived from the FMC, is shown as a magenta coloured line joining the waypoints. The active waypoint — the one you're currently navigating towards — is shown as a magenta coloured star. The other waypoints making up the active route are called inactive waypoints, and they're shown as white stars. Both types are identified by name. At the top of the display, you'll see the distance to the next waypoint and the time at the next waypoint. Now, additional data. Weather radar returns — that's WXR — and range arcs are displayed when the WXR switch is on. Turbulence mode, shown as +T, may be available, as previously described. You'll also see indications of other data such as wind speed and direction, and lateral and vertical deviations from the selected flight path. Here's a clever part — the FMC can predict events. It combines current ground speed and lateral acceleration to show one of two things. During turns, it shows a curved trend vector, which is white. During climb or descent, it shows a range to altitude arc, which is green. Finally, off-route waypoints, airports, and nav aids can all be shown in their relative position to your aircraft's progress and the selected range. And you can select additional waypoint information to be displayed — things like altitude and time. So in summary: the MAP display gives you a moving map with a common scale, a 90-degree compass arc at the top, magnetic or true reference depending on latitude and your selector switch, magenta for the active route and waypoint, white for inactive waypoints, and predictive trend vectors in white or green. That's your complete navigation picture.