Electronic Horizontal Situation Indicator (EHSI)

The Electronic Horizontal Situation Indicator lies at the very heart of the T-6/A Texan II's EFIS system and is the primary navigation aid used by T-6 pilots when flying. The EHSI and EADI make up the core of the EFIS system.

EHSI Composite Mode

In composite mode, the EADI is displayed with an Compass Rose and CDI needle overlayed on top to aid in primary navigation should either the EADI or EHSI display screen fail.

The images below show the EHSI in VOR and GPS controlled composite mode. This is one of the more common modes used for primary navigation and displays a great deal of information at a glance for the pilot.

EFIS Composite Mode can be toggled on or off using the 'CMP' button on the bottom left of either display.

The top left shows the following information;

• Distance in nautical miles from the aircraft to the navigation source (NAV1).
• Current indicated airspeed of the aircraft.
• Estimated time of arrival at the current navigation source.

The top right shows the following information;

• Current navigation course heading set by the pilot in the EFIS system.
• Current heading set by the pilot in the EFIS system.

EHSI in VOR composite mode

The images below show the EHSI in GPS mode. This is one of the more common modes used for primary navigation and displays a great deal of information at a glance for the pilot.

The top left shows the following information;

• Distance in nautical miles from the aircraft to the next GPS waypoint (GPS).
• Current indicated airspeed of the aircraft.
• Estimated time of arrival at the current GPS waypoint.

The top right shows the following information;

• Current Direct To (DTK) heading set by the GPS system.
• Current heading set by the pilot in the EFIS system.

EHSI in GPS composite mode

EHSI HSI Mode

The images below show the EHSI in VOR HSI mode. This is one of the more common modes used for primary navigation and displays a great deal of information at a glance for the pilot.

The top left shows the following information;

• Distance in nautical miles from the aircraft to the navigation source (NAV1).
• Current indicated airspeed of the aircraft.
• Estimated time of arrival at the current navigation source.

The top right shows the following information;

• Current navigation course heading set by the pilot in the EFIS system.
• Current heading set by the pilot in the EFIS system.

EHSI in HSI VOR mode

At the left of the EHSI, the display will show either VOR or GPS depending on what the primary navigation source is set to. As you can see from the image above, it is currently set to VOR. Pressing the 'NAV' button on the EFIS panel will toggle between VOR and GPS mode.

The center of the display shows a standard compass rose along with three needles.

• The main green needle is the VOR course needle and can be adjusted using the 'CRS' knob on the EFIS panel. In GPS mode the arrow is blue as explained further along.
• The white needle displays the direction of the selected navigation source, in this case it is a VOR/DME station located 18.0 nautical miles from the aircraft at a heading of 83 degrees.
• The red needle is the current GPS direction. This needle used with the flight planner facility in FS2004 or FSX will show you the direction to your next GPS waypoint.

At the very bottom of the display are the distances from the aircraft to the selected navigation sources. If no source is found or selected then the display will show '----'.

EHSI in HSI GPS mode

In GPS mode, the EHSI changes colour and function. Instead of showing the same information as in the EHSI VOR mode version, the EHSI now shows the distance from the aircraft to the next GPS waypoint on the left and the suggested 'Direct To' (DTK) bearing on the right.

EHSI Directional Gyro Mode

In directional gyro (DG) mode, the EHSI simply shows the current heading bug as controlled by the pilot via the EFIS panel and a standard compass rose. HSI and DG modes are toggled with the HSI button on the EFIS panel.

EHSI in directional gyro (DG) mode

EHSI ARC Map Mode

In ARC Map mode, the EHSI displays a large scale moving map forward of the aircraft as indicated in the image below.

As with the HSI mode, the top left shows the following information;

• Distance in nautical miles from the aircraft to the navigation source (NAV1).
• Current indicated airspeed of the aircraft.
• Estimated time of arrival at the current navigation source.

The top right shows the following information;

• Current navigation course heading set by the pilot in the EFIS system.
• Current heading set by the pilot in the EFIS system.

EHSI in VOR ARC Map Mode showing VOR's, NDB's and Airports.

In addition, the ARC Map mode shows a deviation bar on the bottom of the screen which acts as a centering needle for the selected navigation source, similar in function to the CDI needle when on HSI mode.

The moving map will ALWAYS display your current flightplan route, however by pressing the ARC button on the EFIS panel you can cycle through the following ARC map display modes.

• ARC Map with VOR stations displayed
• ARC Map with VOR & NDB stations displayed
• ARC Map with VOR & NDB stations and Airports displayed.
• Revert to HSI mode.

When in GPS Mode, the ARC Map alters slightly showing the same information as in the EHSI VOR mode version, the EHSI now shows the distance from the aircraft to the next GPS waypoint on the left and the suggested 'Direct To' (DTK) bearing on the right, along with a CDI needle which is slaved to the current flightplan waypoint.

All other ARC functions as indicated above apply in GPS mode also.

EHSI in GPS ARC Map Mode showing VOR's.

EHSI Standard Map Mode

In normal map mode, the EHSI displays a 360 degree moving map centered on the aircraft as indicated in the image below.

As with the HSI mode, the top left shows the following information when in VOR Nav mode;

• Distance in nautical miles from the aircraft to the navigation source (NAV1).
• Current indicated airspeed of the aircraft.
• Estimated time of arrival at the current navigation source.

The top right shows the following information when in VOR Nav mode;

• Current navigation course heading set by the pilot in the EFIS system.
• Current heading set by the pilot in the EFIS system.

EHSI in GPS ARC Map Mode showing VOR's, NDB's and Airports.

When in GPS Mode as shown above, the map alters slightly showing the same information as in the EHSI VOR mode version, the EHSI now shows the distance from the aircraft to the next GPS waypoint on the left and the suggested 'Direct To' (DTK) bearing on the right, along with a CDI needle which is slaved to the current flightplan waypoint.

Both the MAP and ARC modes can be zoomed from 2nm range out to 500nm range by using the appropriate 'RNG' buttons on the EFIS panel.

Failure Annunciations

If the Heading indicator fails, the display will show below.