What does 'GPS primary lost' mean on the A320?
On the Airbus A320, GPS PRIMARY LOST means the flight-management system no longer trusts GPS as its main position source. In a flight simulator, that usually means degraded lateral guidance, especially for RNAV approaches. Keep flying the aircraft, cross-check raw data, and be ready to use selected modes, radio navigation or a go-around.
What does GPS primary lost actually mean?
GPS PRIMARY LOST means the A320's flight management and guidance system is no longer using GPS as its trusted primary position input.
It does not automatically mean the aeroplane is unflyable. In Airbus logic, the system can fall back to inertial reference and, where the add-on models it, radio updating such as DME/DME or VOR/DME. What changes is your confidence in managed navigation, especially on any arrival or approach that depends on area navigation rather than a ground-based localiser.
Depending on the add-on, you may see the warning on the ND, on MCDU position-monitoring pages, or as a general navigation caution rather than as a dramatic system failure. If you need to decode what the displays are telling you, our explainer on the main A320 cockpit controls and displays is the quickest refresher.
Why does it appear in flight simulators?
In sim use, GPS PRIMARY LOST is often caused by set-up or data problems rather than a neatly simulated satellite failure.
- IRS or ADIRS not ready: if you spawn on the runway, load a turnaround state, or rush the initial set-up, the aircraft may not yet have a stable position solution.
- Repositioning the aircraft: slew mode, instant reposition, some save-and-load states, time acceleration and certain pause behaviours can upset navigation logic.
- Route or navdata mismatch: on more complex A320 add-ons, imported routes or changed procedures can conflict with the aircraft's own database and trigger wider navigation oddities.
- Add-on bugs or conflicts: some aircraft simply mis-handle GPS availability after loading a flight, changing the approach externally, or using conflicting mods.
A mistake we see constantly is treating this as only a flight-plan problem. The magenta line can still be visible while the position source behind it is no longer reliable.
How do you handle GPS primary lost in an A320 simulator?
Treat it first as a guidance-integrity problem, not as a button-pressing puzzle.
- Fly the aircraft first. If the A320 starts wandering in NAV, stabilise it in a mode you can verify. Using selected heading, speed and altitude on the FCU is usually the cleanest way to stop the automation digging a deeper hole.
- Check whether the warning is transient. If it appeared just after spawning, pausing or repositioning, give the systems a moment to settle. If your add-on simulates alignment properly, confirm the inertial system is actually ready.
- Cross-check position. Compare the aircraft's displayed position with the outside view, nearby navaids and the route shown on the ND. If the aeroplane is clearly not where the FMGS thinks it is, do not continue in managed NAV for approach work.
- Decide by approach type. An ILS or LOC approach can usually still be flown using radio guidance. An RNAV or GPS-based approach should normally be treated as unavailable once GPS primary is lost, unless you know your add-on models a valid fallback and you can verify the path independently.
- Fix only the broken part. If the route itself has become scrambled, correct the affected legs in the box rather than rebuilding the entire flight from memory. Our walkthrough on programming the Airbus A320 MCDU/FMS covers the route and approach pages that matter.
- Go around if the approach becomes doubtful. If the lateral path looks wrong, the workload spikes, or you cannot verify where you are, abandon the approach and re-set from a stable position.
If your add-on models MCDU position-monitor pages, use them. They can show whether the FMGS has fallen back to mixed inertial or radio updating rather than suffering a total position loss.
Can you still continue the approach after GPS primary lost?
You can often continue a conventional radio approach, but you should be very cautious about continuing an RNAV or GPS-based procedure.
| Approach type | Usual sim response | Why |
|---|---|---|
| RNAV / GPS / RNP | Usually discontinue | The procedure depends on area-navigation integrity, which is exactly what the message calls into question. |
| ILS or LOC | Usually continue if established and identified | Localiser and glideslope guidance come from ground radio aids, not the GPS position source. |
| VOR / DME | Continue only if you are comfortable on raw data | The guidance can still be valid, but you must verify it yourself rather than trust the magenta line. |
| Visual | Often continue if position awareness is solid | You are no longer depending on FMS navigation for the final path. |
What if the message appears but the aeroplane still tracks the route?
If the route still looks sensible en-route, the system may be using a fallback source or the warning may have been brief. Continue only while you can verify position independently, and do not assume a working magenta line means the RNAV approach remains trustworthy.
If the route or approach data also looks corrupted, correct it in the aircraft rather than in the external planner. Our guide to flying the A320 in Microsoft Flight Simulator from set-up to landing is useful if you want to re-establish a normal workflow before trying the approach again.
When should you go around?
Go around if lateral guidance becomes erratic, you cannot verify your position, the procedure in use is RNAV/GPS, or troubleshooting is starting to steal attention from flying. In the sim, the safest recovery is usually selected heading, a safe altitude, time to rebrief, and then either a conventional approach or another attempt from a stable point.