How do you recognise and handle A320 unreliable airspeed?
Unreliable airspeed on an Airbus A320 means one or more indicated airspeeds cannot be trusted, usually because pitot/static or air-data inputs are faulty or obstructed. Recognise it through conflicting, frozen or implausible speed indications, then disconnect speed-dependent automation, stabilise the aircraft with known pitch and thrust, and follow the aircraft’s unreliable-speed checklist.
What does unreliable airspeed mean on an A320?
The A320’s Air Data References calculate indicated airspeed and Mach from pitot and static pressure. A blocked probe, static-pressure problem, icing, an injected computer failure or a simulation fault can therefore produce missing, frozen or incorrect speed data.
The dangerous case is not always a blank speed tape. Incorrect data can look entirely plausible, leaving the crew to detect it from disagreement between displays or from an aircraft response that does not match the indicated speed. A static-pressure fault may also corrupt altitude and vertical-speed information.
In Aviation & Real-World Flying training, we distinguish unreliable airspeed from a straightforward single-ADR fault. If ECAM identifies one failed ADR while the remaining sources agree and aircraft control is unaffected, follow ECAM. If the indications conflict or make safe control uncertain, use the unreliable-speed procedure.
How do you recognise unreliable airspeed?
Suspect unreliable airspeed when the speed indications disagree with one another, remain frozen after a substantial pitch or thrust change, or conflict with the aircraft’s attitude and energy state. Knowing how to interpret A320 speed-tape and FMA cues makes these contradictions much easier to spot.
| Indication | What it suggests |
|---|---|
| Captain, first-officer and standby speeds disagree | One or more air-data sources are faulty or obstructed. |
| Airspeed freezes despite a major pitch or thrust change | A blocked probe, frozen pressure value or ADR fault is likely. |
| Speed changes abruptly while attitude and thrust remain steady | The change is probably an indication error rather than real acceleration. |
| Stall and overspeed warnings appear at implausible times | Conflicting air-data inputs may be driving the warning systems. |
A red speed flag or an ECAM message such as NAV ADR DISAGREE | Air-data validity or agreement has been lost; exact messages depend on the aircraft standard and simulation. |
| Ground speed differs from indicated airspeed | Not proof by itself: wind and the difference between IAS and true airspeed normally produce a substantial split. |
Autopilot or autothrust disconnection can be another clue, but it is not proof on its own. Check the FMA rather than assuming that an FCU selection is active; our A320 automation troubleshooting explanation covers the other common reasons these systems refuse to engage.
How should you handle A320 unreliable airspeed in a simulator?
If unreliable speed affects safe control, stop chasing the speed tape and establish a known pitch-and-thrust condition. If only one ADR has been positively identified as failed and the remaining information is coherent, follow the simulated ECAM instead of unnecessarily removing working automation.
- Take manual control. Disconnect the autopilot and autothrust, then switch both flight directors off. Their commands can depend on the same suspect air data.
- Set known pitch and thrust. Use the memory values supplied with the simulated aircraft’s QRH or abnormal checklist. Hold attitude using the horizon rather than trying to correct the indicated speed.
- Avoid unnecessary configuration changes. Maintain the existing flap/slat configuration initially and check that the speedbrakes are retracted. Follow the phase-specific checklist for the landing gear and subsequent configuration.
- Stabilise the flight path. Keep the wings level, use smooth inputs and establish a safe climb or level condition before troubleshooting.
- Run the ECAM and QRH procedure. Compare the available air-data sources, identify any clear outlier and isolate or switch sources only when directed. Our explanation of how to work through A320 ECAM actions covers the correct action-and-confirmation discipline.
A commonly taught A320 initial reference is shown below. These are stabilisation values, not universal approach targets; procedure revisions, aircraft condition and the simulated model’s documentation take precedence.
| Flight condition | Initial pitch | Thrust |
|---|---|---|
| Below thrust-reduction altitude | 15° nose up | TOGA |
| Above thrust-reduction altitude and below FL100 | 10° nose up | CLB |
| Above FL100 | 5° nose up | CLB |
A mistake we see constantly is leaving the flight directors on and trying to follow their bars. Another is reacting separately to every stall or overspeed warning. Once air data is suspect, attitude, thrust, configuration and the applicable checklist become the primary references.
Which A320 ADR is faulty?
The captain’s PFD normally uses ADR 1, the first officer’s PFD uses ADR 2, and ADR 3 is available as an alternate source through the air-data switching controls. Compare both PFDs with the standby instrument and look for one clear outlier.
Two sources agreeing does not guarantee that they are correct. Common-mode icing or blockage can make multiple sources fail similarly, while the standby system can also be affected by a physical pressure problem. GPS ground speed is useful as a broad reasonableness check but cannot replace indicated airspeed because it includes wind.
Do not switch ADR pushbuttons off at random. Removing a serviceable source can discard the only good data, trigger further warnings or degrade the flight-control law. Use ADR 3 or isolate an ADR only when ECAM or the unreliable-speed checklist directs it.
Simulator-specific causes and false alarms
In a flight simulator, unreliable airspeed may come from an injected failure, simulated probe icing, incorrect air-data source selection or a simplified aircraft implementation.
- Probe icing: Confirm that PROBE/WINDOW HEAT is configured as the aircraft checklist requires. Clearing the switch condition may not remove an already modelled blockage immediately.
- Failure injection: Check the simulator and add-on failure panels after completing the airborne procedure. Some failures remain latched until explicitly cleared.
- Simplified systems: A basic A320 may fail every display together and may not model independent ADR switching. Use the functionality that the aircraft actually provides.
- Normal IAS, TAS and ground-speed differences: Indicated airspeed normally falls relative to true airspeed with altitude, while wind changes ground speed. That difference alone is not an air-data failure.
- High-altitude speed limits: A shrinking margin between low-speed and overspeed indications can be genuine at high altitude. Check weight, altitude, turbulence and Mach before diagnosing unreliable airspeed.
Landing after an unreliable-airspeed event
If a trustworthy source has been identified, use it while continuing to monitor the other displays. If no source is reliable, use the QRH’s configuration-specific pitch-and-thrust tables, make configuration changes deliberately and monitor attitude, flight path, radio altitude and engine thrust.
Do not invent an approach speed from a suspect tape or continue an unstable final. If the aircraft is not in a known, controlled condition, execute the simulator’s published missed-approach procedure; our A320 go-around technique and mode sequence explains the normal control priorities. Real-world crews must use the approved aircraft and operator procedures rather than generic training values.