What is an HSI, and how do you use it?

An HSI (horizontal situation indicator) combines aircraft heading, selected course and lateral navigation deviation on one display. In our Aviation & Real-World Flying coverage and in 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.

The same reading logic applies to a mechanical HSI, an electronic HSI and the compass rose or arc on a glass-cockpit display. Colours, labels and controls vary by aircraft, so read the displayed source rather than assuming green means radio navigation or magenta means GPS.

What does a horizontal situation indicator 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.

DME is not an inherent part of an HSI. A panel may place distance beside or inside the instrument, but GPS distance to a waypoint and DME slant-range distance from a ground station are not necessarily the same measurement.

The deviation scale is not fixed in miles. VOR deviation is angular and becomes increasingly sensitive near the station, localiser guidance is much narrower, and GPS sensitivity may change between en-route, terminal and approach phases. Our explanation of how heading, course, bearing and track differ covers the terms that simmers most often confuse here.

How do you use an HSI with a VOR?

To track a VOR with an HSI, select the appropriate NAV receiver, tune and identify the station, set the intended course, confirm TO or FROM, and intercept the displaced deviation bar. For the radio controls themselves, see our practical NAV1 tuning and interception workflow.

1. Select the navigation source. Confirm that the HSI is displaying the receiver you intend to use, such as NAV1. Tuning one receiver achieves nothing if the instrument remains connected to GPS or another radio.
2. Make the signal valid. Put the VOR frequency in the active position, identify the station where that function is modelled, and check that no NAV, OFF or failure flag is displayed.
3. Set the course, not simply the radial. VOR radials extend away from the station. To fly inbound on the 090 radial, select 270° and expect TO; to fly outbound along that radial, select 090° and expect FROM.
4. Check heading alignment. Compare the HSI with the aircraft's other heading reference. A traditional unslaved or drifting instrument may need manual synchronisation with the magnetic compass.
5. Intercept the course. When established broadly in the selected direction, turn towards the displaced bar. An intercept angle of roughly 20–45° is normally practical; use less when close to the course.
6. Track rather than chase. Reduce the intercept as the bar approaches centre, then hold it there with small wind-correction headings. The required heading may differ from the selected course because of crosswind.

Near VOR station passage, the indication can become very sensitive or briefly unreliable while TO changes to FROM. Hold the expected heading rather than chasing a rapidly moving bar. An NDB may drive a bearing pointer on the HSI, but it does not normally drive the course-deviation bar.

How do GPS, ILS and NDB use the HSI?

The selected navigation source determines what the deviation bar represents and whether the course control changes the guidance.

A glass display can show a radio bearing pointer while its main deviation bar follows GPS. Always verify the source label; our guide to switching an aircraft between GPS and NAV1 explains the selector error behind many apparently dead instruments.

Using the HSI with GPS

With GPS selected, the deviation bar represents the active flight-plan leg or approach path. Confirm the displayed waypoint or leg because loading a route does not always activate it. Turning the course knob may have no effect when the navigator computes the desired track automatically; manual selection requires a supported OBS or course mode.

Using the HSI for an ILS

For an ILS, set the published front-course heading and use the deviation bar for localiser alignment and the glideslope pointer for vertical guidance. The course setting orients the display and may support autopilot capture, but it does not move the fixed localiser beam.

Localiser guidance is more sensitive than VOR guidance, so make small corrections. Do not apply the simple “fly towards the bar” rule from behind the localiser. A back-course procedure requires the sensing or autopilot mode specified for that aircraft, and normal glideslope guidance should not be expected.

How is an HSI different from a CDI?

An HSI combines a course-deviation indicator with the aircraft's heading display, while a conventional CDI presents left-right deviation separately from the heading indicator. The rotating presentation makes intercepts easier to visualise and reduces reverse-sensing errors, but it cannot correct a wrong source, reciprocal course or invalid signal.

Does the autopilot automatically follow the HSI?

The autopilot follows HSI guidance only when the correct lateral mode is armed or engaged and the selected navigation source is valid. The heading bug normally commands HDG mode, while the deviation bar supplies guidance to NAV, LOC or APPR mode.

A common technique is to intercept using heading mode, then arm the appropriate navigation mode for capture. Check active and armed mode annunciations: some autopilots will not capture cleanly when the aircraft is parallel to the course, moving away from it or approaching at an excessive angle. Our guide to what the course selector controls explains why the course arrow, heading bug and autopilot modes must not be treated as one setting.

Why is the HSI not working in a simulator?

Most dead or misleading HSI indications come from source selection or incomplete navigation setup rather than a failed instrument.

• No bar movement or a warning flag: check avionics power, GPS versus NAV/VLOC, NAV1 versus NAV2, the active rather than standby frequency, reception range and terrain line of sight.
• Centred bar but the wrong route: confirm the active GPS leg, selected VOR course and TO/FROM indication. A centred bar does not prove that the intended course is selected.
• The course knob does nothing: GPS may be setting the track automatically, or the simulator control assignment may operate a different course selector.
• The localiser appears reversed: set the published front course and confirm that the aircraft is approaching the correct side. Use a supported back-course mode where required.
• The aircraft zigzags across the course: stop turning directly at the bar. Establish one intercept, reduce it before centring, and allow each small wind correction time to take effect.
• The autopilot will not capture: verify the source, valid signal, armed mode and intercept geometry. Moving the heading bug alone does not select a navigation course.
• The compass card disagrees with the aircraft: synchronise an unslaved gyro and check for simulated gyro drift, an instrument failure, or a magnetic-versus-true heading difference.

How should you practise HSI navigation?

The clearest practice exercise is one manual VOR intercept in calm conditions before adding wind, GPS or autopilot coupling.

1. Choose a nearby VOR within reliable reception range and begin offset from a simple inbound course.
2. Tune and identify it, select the inbound course and verify a TO indication.
3. Intercept manually at about 30° while holding altitude and airspeed.
4. Reduce the intercept as the bar centres, then note the heading required to keep it centred.
5. Repeat with a crosswind, followed by the same exercise using an active GPS leg.

The heading and course numbers do not need to match. Successful HSI navigation means holding the deviation bar near the centre with stable corrections while the intended source and guidance remain valid.