Learn what an HSI shows, how to select VOR, GPS or ILS guidance, intercept and centre a course, and fix common flight-simulator errors.
An HSI (horizontal situation indicator) combines aircraft heading, selected course and lateral navigation deviation on one display. In real-world aviation and flight simulators, select the correct navigation source, set or confirm the desired course, then intercept it until the deviation bar is centred. Check source and validity indications first.
In our Aviation & Real-World Flying coverage, the same reading logic applies to a mechanical HSI, an electronic HSI and the HSI inset on a glass-cockpit primary flight display. Colours, labels and controls vary, so read the displayed source rather than assuming that green always means radio navigation or magenta always means GPS. Our overview of radio, GPS, flight-director and autopilot guidance explains what supplies the information shown on the HSI.
What does an HSI show?
An HSI shows the aircraft's heading and its position relative to a selected navigation course. It is a spatial presentation rather than a moving map: the aircraft symbol normally remains fixed while the compass card rotates beneath it.
| HSI element | What it means |
|---|---|
| Compass card and heading index | The aircraft's heading, normally magnetic unless the avionics are configured otherwise. |
| Course arrow | The selected VOR course, localiser front course or displayed GPS desired track. |
| Course-deviation bar | Shows whether the selected course lies left or right of the aircraft. Centred means the aircraft is on that course, not necessarily pointing along it. |
| TO/FROM indication | For VOR guidance, shows whether the selected course leads towards or away from the station. It is not normally relevant to a localiser. |
| Heading bug | A heading reference used by the pilot and, in heading mode, by the autopilot. It is separate from the navigation course. |
| Bearing pointer | Points towards a selected VOR, ADF or GPS waypoint. It does not show course deviation. |
| Glideslope pointer | When fitted and receiving an ILS, shows whether the aircraft is above or below the vertical path. |
| Source or warning flag | Identifies inputs such as NAV1, NAV2, GPS or FMS, and warns when guidance is invalid. |
The deviation scale is not a fixed distance scale. VOR deviation is angular and becomes increasingly sensitive near the station, localiser guidance is much narrower, and GPS sensitivity can change automatically between en-route, terminal and approach phases.
How do you use an HSI with a VOR?
To use an HSI with a VOR, tune and identify the station, select the correct NAV receiver, set the intended course, confirm TO or FROM, then intercept and track the deviation bar.
- Select the navigation source. Confirm that the HSI is using the receiver you intend, such as
NAV1. A correctly tuned frequency is useless if the display is still set to GPS or another receiver. - Make the signal valid. Put the VOR frequency in the active position and identify the station where applicable. Check that no NAV, OFF or failure flag is displayed.
- Set the desired course. VOR radials extend away from the station. To fly inbound on the 180 radial, for example, select 360° and expect a TO indication; to fly outbound on that radial, select 180° and expect FROM.
- Check heading alignment. A manually aligned or drifting heading system can make the HSI picture misleading. Compare it with the aircraft's other heading reference and synchronise it if the installation requires this.
- Intercept the course. For normal VOR guidance, turn towards the displaced deviation bar. An intercept angle of roughly 20–45° is usually practical, with a shallower angle when close to the course or using a sensitive localiser.
- Track rather than chase. As the bar approaches the centre, reduce the intercept angle and establish the required wind-correction heading. Make small corrections; do not repeatedly turn directly at the needle.
The deviation bar shows where the selected course lies, not where the station itself lies. Near VOR station passage, the indication can become very sensitive or briefly unreliable and the TO/FROM indication will change. Hold the expected heading rather than chasing a rapidly moving bar.
For worked examples of course selection, interception and tracking, see our practical guide to using VOR and NDB equipment in flight simulators. An NDB may feed a bearing pointer on an HSI, but it does not normally drive the course-deviation bar.
How do GPS and ILS indications differ?
GPS, VOR and ILS can all drive the same HSI, but their source selection and course behaviour differ.
| Source | Set-up | What the course control does |
|---|---|---|
| VOR | Tune the station, select NAV and identify it. | Selects the VOR course and determines the TO/FROM presentation. |
| GPS/FMS | Select GPS or FMS and activate the required flight-plan leg or approach. | Usually does not change an active GPS leg unless a specific OBS or course mode is selected. |
| ILS localiser | Tune the localiser, select NAV/VLOC and set the published inbound course. | Orients the display and may support autopilot capture, but it does not change the fixed localiser beam. |
Using the HSI with GPS
With GPS selected, the HSI deviation bar represents the active flight-plan leg or approach path. Confirm the waypoint or leg displayed by the navigator; merely loading a route does not always activate it.
A common source of confusion is turning the course knob and seeing no change. That is often normal because the GPS computes the desired track. Some systems allow manual course selection in OBS mode, but the exact behaviour depends on the navigator and aircraft.
Using the HSI for an ILS
For an ILS, select NAV or VLOC, activate the localiser frequency and set the published front-course heading. Use the lateral deviation bar for localiser alignment and the separate glideslope pointer for vertical guidance.
Localiser guidance is much more sensitive than VOR guidance, so use small corrections. Do not apply the simple “fly towards the bar” rule to the rear of a localiser or an ILS back-course procedure without understanding the installation's sensing. Use a supported back-course mode where specified, and do not expect normal glideslope guidance on a back course.
How is an HSI different from a CDI?
An HSI combines a course-deviation indicator with the aircraft's heading display. A conventional CDI presents left-right deviation separately from the heading indicator, so the pilot must mentally relate the selected course to the aircraft's orientation.
The rotating HSI presentation makes intercepts easier to visualise and reduces common reverse-sensing mistakes, but it does not make the underlying navigation signal more accurate. A wrong source, reciprocal course or invalid signal still produces wrong or misleading guidance.
Does the autopilot automatically follow the HSI?
The autopilot follows HSI guidance only when the appropriate mode is armed or engaged and the selected navigation source is valid. The heading bug normally controls HDG mode, while the course-deviation bar supplies lateral guidance to NAV, LOC or APPR mode.
Centred guidance alone does not prove that the autopilot will capture it. Check the active and armed mode annunciations, use a sensible intercept angle, and ensure GPS is selected for a GPS leg or NAV/VLOC for radio guidance.
Why is the HSI not working in a simulator?
Most dead or misleading HSI indications come from a source-selection error rather than a failed instrument.
- No deviation-bar movement: check for GPS instead of NAV/VLOC, the wrong NAV receiver, a frequency left in standby, an inactive GPS leg, excessive VOR range or terrain blocking line of sight.
- Full-scale or apparently reversed guidance: confirm the selected course, TO/FROM indication and whether the aircraft is receiving the front or rear side of a localiser.
- The course knob does nothing: GPS may be controlling the desired track automatically. Select VOR/LOC or the navigator's supported OBS mode if manual course selection is required.
- The autopilot will not capture: verify the source, valid signal, armed NAV or approach mode and intercept geometry. The heading bug by itself does not select a navigation course.
- The compass card disagrees with the aircraft: synchronise an unslaved directional gyro or check whether simulated gyro drift or an instrument failure is enabled.
Microsoft Flight Simulator users can follow our VOR source-selection and dead-CDI troubleshooting checks when a tuned station produces no usable HSI guidance.