# HORIZONTAL SITUATION INDICATOR (HSI)
### HORIZONTAL SITUATION INDICATOR (HSI) DISPLAYS AND ANNUNCIATORS
* Heading display on the HSI has 3 selectable modes: Full compass, Arc, and Map mode.
* Modes are selected by pushing the HSI button.
### FULL COMPASS MODE
* Displayed on initialization.
* 360-degree compass view
* Present heading is indicated by a fixed lubber  line at the top of the heading scale with a digital heading readout directly above the lubber line.
### ARC MODE
* 90 degrees of compass view.
* Weather is displayed when the WX button is pushed.
* When the heading bug goes beyond the display range is displayed and shows the shortest direction to the heading select bug.
### MAP MODE
* 90 degrees of compass view.
* Weather is displayed when the WX button is pushed.
* Flight plans are displayed
* Cannot be used for preview mode.
### SELECTED HEADING DIGITAL READOUT AND BUG
* Displays the digital value for the aircraft selected heading.
* Cyan heading select bug is positioned by rotating the HDG SEL knob.
* Pushing the PUSH SYNC button on the HDG SEL knob synchronizes the heading bug and readout to the current aircraft heading.
* When the aircraft selected heading (or the referenced aircraft heading) is invalid, the bug is removed, and digital readout is replaced with 
### DRIFT ANGLE BUG
* Represented by an inverted solid white triangle displayed on the outside edge of the heading scale.
* The difference between the aircraft heading and the aircraft ground track is the drift angle.
* The drift angle bug is placed on the edge of the heading scale and aligned to the drift angle with respect to the lubber line.
* When the drift angle is 0 degrees, the drift bug fits inside the heading bracket notch.
### PRIMARY NAV SOURCE ANNUNCIATOR
* Selected using the **V/L** or **FMS** buttons.
* The **V/L**(VOR/LOC) button selects the available SRN (short-range navigation) source, displayed in green.
* The associated annunciators are 
* The **FMS**button selects FMS as the source, displayed in magenta.
* With dual FMS systems installed the identifier will show 
* When both sides have the same NAV source selected, digital readout for all information turns amber.
### PRIMARY NAV DISTANCE IDENTIFIER
* Displays the NAV source station identifier.
* The next magenta TO waypoint identifier is displayed.
### PRIMARY NAV DISTANCE READOUT
* Distances of 100 NM or more, the digits are displayed with 1 NM resolution
* Distances of less than 100 NM, the digits are displayed with 0.1 NM resolution
### PRIMARY NAV ESTIMATED TIME ENROUTE
* Time is always displayed in minutes.
### HEADING SOURCE ANNUNCIATORS
* Selected by the IRS reversion buttons.
* Not displayed when the on-side IRS source and magnetic heading are selected.
### COURSE SELECT/DESIRED TRACK POINTER AND READOUT
* Green for VOR and LOC navigation and the label is 
* When VOR or LOC is selected, the track pointer is positioned by turning the CRS knob.
* When the PUSH DIR button in the center of the CRS knob is pushed, the course select value is set to the course that minimizes the lateral deviation.
* Magenta for FMS navigation and the label is 
* Value of the desired track is supplied by the FMS.
* Course deviation bar moves laterally and shows lateral deviation.
* If both sides have the same navigation source selected the pointer, deviation bar, and digital readout turn amber.
### TO/FROM INDICATOR
* Magenta for FMS, Green for VOR or LOC. Turns amber if both sides are selected to the same source.
* Pointer indicates the aircraft is flying to or away from the selected navigation source.
* For a TO indication the triangle is located above the nose of the aircraft symbol.
* The FROM indication is a triangle pointer on the tail of the aircraft symbol.
### COURSE DEVIATION INDICATOR (CDI) AND LATERAL DEVIATION SCALE
* Only displayed when a navigation source is active.
* Deviation bar moves left or right to show the deviation from the selected NAV source.
* When the back course mode is selected, or when tuned to a localizer frequency and the selected course is more than 100 degrees from the aircraft heading, the course deviation automatically reverses to properly sense deviation with respect to the course centerline.
* When lateral deviation data is invalid, the CDI is removed and  is displayed in the CDI scale area.
### BEARING POINTERS
* Source is either VOR, ADF, or FMS.
* Source is selected using the buttons on the guidance panel.
### GROUNDSPEED
* Displayed in the upper left corner of the HIS just below the airspeed tape.
* When the IRS is invalid the digits are replaced with 
### DME SOURCE ANNUNCIATOR
* DME source is selected by pushing the V/L button.
* DME source annunciation reflects the short-range navigation source selection.
* VOR1/LOC1 displays  VOR2/LOC2 displays 
* When primary NAV source is FMS, the last selected VOR/LOC is used for the DME distance display.
* When the same source is used, the DME data is displayed in amber.
### DME STATION IDENTIFIER, DISTANCE, AND TTG READOUT
* DME source station identifier is displayed directly below the DME source annunciator.
* Distance to go to the waypoint identified by the DME station identifier is shown in nautical miles.
* TTG to the waypoint identified by the DME station identifier is shown in minutes.
* When DME is in DME hold mode  is displayed in the front of the distance readout.
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