What are EADI and EHSI displays, and how do pilots use them?
EADI and EHSI displays explained: see what each instrument shows, how pilots scan them together, and how to avoid source and mode errors.
EADI means Electronic Attitude Director Indicator: it combines attitude, flight-director commands and key flight data for controlling the aircraft. EHSI means Electronic Horizontal Situation Indicator: it combines heading, course and navigation information for positional awareness. In real-world aviation, pilots scan both together rather than treating either display as a complete picture.
Both are components of an electronic flight instrument system, or EFIS. Their exact layout, terminology and colours vary by aircraft generation and manufacturer, but their basic division of work remains consistent.
What does each electronic display show?
The simplest distinction is that the EADI is primarily a flight-control reference, while the EHSI is primarily a navigation reference.
| Display | Main purpose | Typical information |
|---|---|---|
| EADI | Shows how the aircraft is flying and what guidance is commanding | Artificial horizon, pitch ladder, bank angle, aircraft symbol, slip or skid, flight-director bars and ILS deviation. Later designs may add airspeed, altitude, vertical speed, radio altitude, minima and flight-mode annunciations. |
| EHSI | Shows where the aircraft is heading and its position relative to the selected route or radio aid | Compass rose or arc, heading, track, selected heading, course pointer, course deviation, bearing pointers, distance and TO/FROM information. Map modes may add waypoints, range rings, wind and weather-radar returns. |
The EHSI does not normally calculate the route itself. It presents information supplied by sources such as the flight-management system, GNSS, VOR, DME or ILS receiver. Our explanation of how navigation sources produce course and position guidance covers what sits behind those indications.
Three terms often cause confusion: heading is where the nose points, track is the aircraft’s path over the ground, and course is the desired line being flown. Wind can make all three different.
How do pilots use EADI and EHSI together?
Pilots use a repeating attitude-guidance-navigation scan, controlling the aircraft on the EADI and checking the resulting path on the EHSI.
- Verify the setup. Check the navigation source, active route leg, selected course, heading bug, map range and orientation. Confirm which flight-director and autopilot modes are active or armed.
- Control attitude on the EADI. Set pitch and bank using the horizon and aircraft symbol, then cross-check airspeed, altitude and vertical performance. Flight-director bars may be followed only after confirming that they represent the intended mode.
- Check the path on the EHSI. Compare heading and ground track with the desired course, route line or radio-navigation deviation. A crosswind may require the aircraft to point away from the desired track.
- Make a measured correction. Use the EHSI to judge which way and how far the aircraft is displaced, but make the actual pitch and bank change against the EADI. Avoid chasing a moving needle with abrupt control inputs.
- Cross-check independent information. Compare the electronic indications with standby instruments, raw radio data and the other pilot’s display where fitted. Automation may use the same faulty source, so an engaged autopilot is not an independent check.
The weighting changes with the phase of flight. During a turn, climb or turbulent approach, the EADI receives tighter attention; during route monitoring, intercepts and holding, the EHSI receives longer glances. Neither replaces an outside scan in visual conditions.
For simulator practice, our guide to building a core flight-instrument scan in Microsoft Flight Simulator shows how attitude, speed, altitude and heading cross-checks transfer from conventional instruments to glass displays.
How are EADI and EHSI used on an ILS approach?
On an ILS approach, the EHSI primarily supports lateral alignment while the EADI presents attitude, flight-director guidance and usually both localizer and glideslope deviation.
Pilots first confirm that the correct ILS source is selected and identified, with the inbound course set where the installation requires it. They monitor localizer interception on the EHSI or repeated EADI scale, then use the EADI’s glideslope indication to manage the vertical path. The flight-mode annunciator must show the expected localizer and glideslope modes armed or captured.
A programmed map line is not proof that an ILS signal has been captured. Likewise, centred deviation bars show alignment with the selected signal, not necessarily that the correct runway, frequency or approach has been chosen.
Are EADI and EHSI the same as PFD and ND?
Broadly, the EADI developed into the attitude-and-guidance portion of the modern primary flight display, while the EHSI developed into the navigation display.
The terms are not exact synonyms. Earlier EFIS installations often had dedicated EADI and EHSI units; a modern PFD and navigation display usually include more information and can support reversionary layouts. Our overview of A320 PFD and navigation-display functions provides a useful example of the modern arrangement.
What EADI and EHSI mistakes cause confusion?
Most EADI and EHSI errors come from trusting a plausible-looking indication without checking its source, mode or scale.
- Wrong navigation source: the display may be following the flight-management route when the pilot expects VOR or ILS guidance. Read the source annunciation rather than relying on needle colour or shape.
- Unverified flight-director mode: command bars can give perfectly valid commands for the wrong selected mode. The flight-mode annunciator is the key indication of what the automation is actually doing.
- Heading, track and course confusion: turning the heading bug does not change the selected radio course, and wind means heading may not match track.
- Unsuitable map range: a range that is too large hides local deviation and waypoint detail; one that is too small hides the broader route and upcoming turns.
- Display fixation: staring at the EHSI can allow pitch or bank to drift, while staring only at the EADI can leave the aircraft accurately controlled but following the wrong route.
- Assuming colours are universal: manufacturers use different conventions for active, armed, selected and managed guidance. Pilots learn the symbology for the specific aircraft rather than transferring assumptions from another cockpit.
A mistake we see constantly in flight simulation is following a convincing magenta route without confirming the active waypoint and navigation source. The same discipline applies in real aircraft: identify what generated the indication before acting on it.
What if an EADI or EHSI fails or disagrees?
A blank, frozen or disagreeing display must be treated as either a display-unit failure or a sensor and data-source failure until the crew identifies which one has occurred.
If only the screen or display unit has failed, reversionary controls may place essential attitude or navigation information on another screen. If an attitude sensor, heading reference or navigation receiver has failed, moving the same data to another display will reproduce the bad information. Pilots compare independent displays and standby instruments, observe failure or comparator messages, maintain control using a reliable reference and follow the aircraft’s approved abnormal checklist.