Horizontal Situation Display

Horizontal Situation Display
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Cockpit art courtesy of Cockpits.nl

The Horizontal Situation Display (HSD) is one of the most important pages available on your MFD. It is a moving-map display of the current horizontal situation around you, showing friendly and enemy aircraft, the route you are flying, the area being scanned by your radar, and many other useful pieces of information. The HSD is used to maintain situational awareness of your present location and of what is happening around you.

Basic Symbology

You can imagine the HSD as what you would see if you were directly above your aircraft, looking straight down. There are three range rings, each representing one third of the currently selected display range (so for example, if you have selected 15 miles, each ring is another increment of 5 miles. If you have selected 60 miles, each ring is another increment of 20 miles). Your aircraft is in the center of these range rings, and the map is oriented so that your aircraft's heading is straight up. Each range ring has four spokes, representing north, east, west, and south. The north spoke on the innermost range ring is replaced with a solid white triangle, to show you what your heading is.

Your navigational course is displayed on the HSD. Each steerpoint is displayed as white shape, with the currently selected steerpoint flashing. The shape of the steerpoint symbol depends on the type of steerpoint - normal steerpoints are circles, insertion points are squares, and target/CAP steerpoints are triangles. A white line is drawn between each steerpoint, giving you a birds-eye view of your complete flight path. You can navigate to a particular steerpoint simply by turning so that the steerpoint is located directly above your aircraft on the HSD, and then flying that heading.

The area that your radar is scanning is displayed using a cyan box, taking into account your sweep angle, selected range, and antenna orientation. A "ghost cursor" is also displayed, which shows the geographical area that your radar cursor is currently in. This is useful for getting a sense of what area your radar is looking at, and can also be used to help identify targets (if you have a radar spike in a portion of the radar scan area that is over known enemy locations, it's probably an enemy). Note that the scan area can extend further than the HSD displays, in which case the cyan lines will simply continue off the HSD.

Known enemy positions are uploaded into your aircraft's computer before you take off - these are displayed in yellow. Some threats have a circle around them representing the effective range of the threat (for example, SAM sites will show the maximum range the missile can hit). The circle and thread will turn red once you enter this range. The positions of your wingmen are also displayed in teal.

The following diagram from the F-16 MLU avionics manual describes the basic symbology used by the HSD. Some items also apply to the FCR display.

HSD Symbology
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Other Symbols

The HSD has some navigation/positioning symbology that it shares with the FCR. If the position of the bullseye is visible on the HSD, it will be displayed with a graphic that looks like… a bullseye. There is also a cue in the bottom left of the screen which displays a navigational/positional reference. If bullseye mode is selected, it will display the bullseye cue (see the bullseye page for more information). If bullseye mode is not selected, it displays a cue which looks like a W shape with a line going through it. The position of the reference line indicates your deviation from the steerpoint course you are on (the concept is similar to a VOR CDI if you are familiar with general aviation). You can think of the spike in the center of the W as your airplane, and the position of the vertical line as the position of the steerpoint course relative to your aircraft. For example, in the picture below, you can see that the aircraft is to the right of the steerpoint course, so the vertical line is diverted to the left. You would have to turn to the left to get back on course.

HSD Navigation Cue
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Cockpit art courtesy of Cockpits.nl

Note: the numbers above the steering cue are your bullseye position (in this case, bullseye 035 at 19 miles).

OSB Functions

HSD OSB Options
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Cockpit art courtesy of Cockpits.nl

The HSD has the OSB configuration seen in the picture above. Each OSB's function is summarized in the table below.

Abbreviation Description
DEP There are two view positions that the HSD can use. In the default mode (DEP), your aircraft's position and the center of the range rings are depressed to about 1/3rd of the height of the screen. This gives you a better view of what is in front of the aircraft (since you are usually more interested in what's in front of you than what's behind you). In the second view mode (CEN), your aircraft is positioned in the center of the MFD, so that you can see the same distance in all directions. Pressing this OSB toggles between these two modes.
DCPL Your HSD range can be either decoupled (DCPL) or coupled (CPL) to the FCR range. If coupled, the HSD will automatically scale so that it shows the same distance as the FCR, and if decoupled, you can manually select the range. Pressing this OSB toggles between these two modes.
NORM Pressing this OSB toggles the current zoom level on the HSD. You can select NORM (normal view), EXP1 (area around your aircraft is expanded), and EXP2 (area around your aircraft is expanded even more).
CNTL This opens the HSD control menu (see below).
FRZ If this OSB is selected, the HSD will freeze in its current position, and will not turn with your aircraft or reposition itself to keep you centered. This is useful to give yourself a static view of a particular area. Remember to deselect this before you fly off the HSD!
DCLT Pressing this OSB will declutter the display, removing some information to make the map easier to read.
Up/Down These OSBs are displayed on the top two buttons on the left row. Pressing up will increase the range displayed on the HSD, and pressing down will decrease the range. If you cannot increase or decrease the range any more, the arrow symbol will disappear. These OSBs are only available if the range is decoupled from the FCR (see above).

HSD CNTL Menu

HSD CNTL Menu
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Cockpit art courtesy of Cockpits.nl

When you press the CNTL OSB on the main page, the OSB configuration changes to allow you to select which information you want displayed on the HSD. Each OSB can be toggled to turn the associated item on/off. The OSBs have the functions listed below…

Abbreviation Description
FCR Toggles display of the radar scan area and the "ghost" cursor showing the position of your FCR cursor.
PRE Toggles the display of enemy targets that were programmed into your aircraft's computer before takeoff.
AIFF Toggles the display of IFF responses from other aircraft.
CNTL Leaves the CNTL menu and returns you to the main page.
LINE 1 - 4 Toggles the display of map information lines on the HSD. Currently LINE 1 is the only line with any information - it shows the FLOT (forward line of troops).
RINGS Toggles the display of range rings around your aircraft.
ADLNK Toggles the display of threats uploaded to your computer from an air data link (such as an AWACS aircraft).
GDLNK Toggles the display of threats uploaded to your computer from a ground data link.
NAV 1 - 3 These toggle the display of your navigational routes. Only NAV 1 has any information - it shows the flight path for your mission.

HSD as SOI

The FCR is usually the sensor of interest (indicated by the green border around its MFD page). However, you can also select the HSD as the SOI by pressing down on the DMS switch. If the HSD is selected, you can slew a cursor around using your cursor switch. This makes the following functions available…

  • Put the cursor over a waypoint and press up on the TMS switch to designate it as the active waypoint.
  • Put the cursor over a threat and press up on the TMS switch to activate its range ring (if it's not already displayed).
  • Put the cursor over a threat and press down on the TMS switch to deactivate its range ring (if it's active).
  • Slewing the cursor past the top or bottom of the screen will bump the selected range (just like the FCR).
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