What is the Airbus A320 ISIS, and how is it used in a sim?
The Airbus A320 ISIS (Integrated Standby Instrument System) is an independent backup display for attitude, airspeed and altitude. In Aviation & Real-World Flying and A320 simulation, it is used to cross-check the primary displays, set standby barometric pressure, show ILS guidance where supported, and retain essential references after a display failure.
What does the A320 ISIS display?
The ISIS combines the functions of a standby attitude indicator, airspeed indicator and barometric altimeter in one electronic unit. It normally has dedicated attitude sensing and standby pressure inputs rather than merely copying either pilot's PFD.
| Indication | What it provides |
|---|---|
| Attitude | A pitch-and-bank horizon for controlling the aircraft when primary attitude displays are unavailable or suspect. |
| Airspeed | An indicated-airspeed tape, with Mach and reference bugs on units or add-ons that model them. |
| Altitude | Barometric altitude and the independently selected pressure reference. |
| ILS | Raw localiser and glide-slope deviation when an ILS is tuned, its signal is valid and the ISIS landing-system display is selected. |
It is not a miniature replacement for the complete PFD and ND. Flight-director bars, flight-mode annunciations, navigation maps, engine indications and system pages are not part of its core job. Our guide to reading the PFD's attitude, speed and altitude tapes explains the primary indications against which ISIS should be checked.
Aircraft standards differ. Older A320 panels and some simulator aircraft use three separate standby instruments instead of an electronic ISIS, while less detailed add-ons may render the ISIS as a decorative or partly functional display.
How do you use ISIS during a normal A320 flight?
In normal operation, use ISIS as an independently set cross-check rather than as the primary flying display.
- Power and initialise it. After electrical power is established, allow the display to complete its self-test or alignment. Do not taxi with invalid attitude or air-data flags still visible.
- Cross-check the indications. Confirm that pitch and bank agree with the aircraft's position on the ground, the airspeed is plausible and the indicated altitude is close to the expected field elevation after setting local pressure.
- Set the standby barometric pressure. Use the ISIS BARO control rather than assuming the PFD setting or simulator altimeter shortcut has updated it. Select local QNH as required, STD at the transition altitude, then local pressure again when descending through the transition level.
- Recheck it at useful points. Compare ISIS with both PFDs before take-off, after pressure changes and during approach preparation. This check fits naturally into our normal A320 cockpit and checklist sequence.
- Select ILS indications when needed. Tune the ILS through the aircraft's normal navigation-tuning method, then activate the ISIS LS display if the model supports it. The LS control displays received guidance; it does not tune the frequency.
A common error is setting QNH on both PFDs but leaving ISIS on STD or an old pressure value. That produces a convincing altitude disagreement even though nothing has failed. Also check whether the unit is displaying hPa or inHg before diagnosing a fault.
On detailed models, the EFIS-panel LS pushbutton and the ISIS landing-system selection are separate. If the PFD shows localiser and glide-slope diamonds but ISIS does not, inspect the ISIS control before retuning the approach.
How do you fly using ISIS after a PFD failure?
After one PFD fails, use the remaining valid PFD as the primary reference and ISIS as the independent cross-check; transfer to an ISIS-centred raw-data scan only when the normal displays are unavailable or unreliable.
- Control attitude first. Establish a known pitch and bank, then include airspeed and altitude in a short repeating scan. Fixating on either tape usually causes larger attitude deviations.
- Compare all available sources. If two attitude displays agree and one differs, that agreement helps identify the suspect source. It is not absolute proof where a common sensor or power failure is possible, so follow the modelled abnormal procedure.
- Use known pitch and thrust for unreliable speed. The standby pitot and static system may provide useful independent data, but icing, blockage or simplified simulator modelling can affect it too. Do not accept the ISIS speed merely because it is on the standby display.
- Treat ILS needles as raw guidance. ISIS does not provide flight-director commands or autopilot mode awareness. Make small corrections, maintain a disciplined instrument scan and abandon an unstable approach.
The ISIS itself does not drive the autopilot or restore failed sensors. If an ECAM alert accompanies the display problem, follow its priorities rather than improvising; our explanation of how to interpret A320 ECAM messages and actions covers that workflow.
Why is the ISIS blank or incorrect in a simulator?
Most simulator ISIS problems come from electrical state, brightness, pressure settings, missing ILS conditions or limited add-on modelling.
| Symptom | Likely cause and fix |
|---|---|
| Blank screen | Establish the required aircraft electrical power, increase ISIS brightness and allow initialisation to finish. If it remains blank, confirm that the chosen aircraft actually models the unit. |
| Altitude differs from the PFD | Match QNH or STD and check hPa versus inHg. A small difference may reflect modelling tolerance; a large persistent error can indicate a simulated static-system fault. |
| No localiser or glide-slope | Confirm that the correct ILS is tuned, the aircraft is within usable signal range and geometry, and the ISIS LS display is selected. |
| Failure also disables ISIS | The add-on may share display data or simplify the electrical and sensor architecture. A PFD display failure, ADR failure and blocked standby probe are different scenarios and should not produce identical results in a fully modelled aircraft. |
| BARO or LS control does nothing | The cockpit hotspot may use a different mouse action, or that function may not be implemented. Generic simulator key commands do not always operate the independent standby controls. |
For an initial practice session, choose a simple PFD display failure so the ISIS remains valid. Once the scan is comfortable, try an air-data failure and decide which source is trustworthy rather than assuming standby data is always correct. The technique relies on the disciplined raw-data scan used for simulator IFR, especially when outside visual references are removed.