Learn why your flight simulator altimeter shows the wrong altitude and fix QNH, QFE, STD mode, pressure units, weather and datum errors.
An altimeter usually shows the “wrong” altitude because its barometric reference is wrong, not because the instrument is broken. In real-world aviation and flight simulators, check local QNH, pressure units, QFE or STD mode, the active weather source and the altitude datum being compared; each can produce a valid but different number.
What altitude should a barometric altimeter show?
With local QNH set, a barometric altimeter should indicate altitude above mean sea level and read approximately the published aerodrome elevation while the aircraft is on the ground. It does not normally show height above the runway or terrain.
| Setting or source | Reference | Expected ground indication |
|---|---|---|
| QNH | Mean sea level | Approximately the aerodrome or runway elevation |
| QFE | Airfield pressure datum | Approximately zero at the reference point |
| STD | 1013.25 hPa or 29.92 inHg | Pressure altitude, which may differ substantially from aerodrome elevation |
| Radio altimeter | Terrain directly below | Approximately zero on the ground |
The published aerodrome elevation may not equal the elevation of your parking stand or runway threshold. Runway slope, scenery mesh and the charted elevation reference can account for a modest difference. If the confusion arose while flying a circuit, our explanation of how circuit height, QNH and airport elevation fit together covers that distinction.
For the underlying pressure references, see our guide to QNH, QFE and standard pressure and their effect on indicated altitude.
How do I correct a wrong altimeter reading?
Correct the reading by matching the altimeter datum and pressure setting to the active simulator weather, then checking that every cockpit instrument received the same setting.
- Identify the value being compared. Decide whether the other number is airport elevation, altitude above mean sea level, height above ground, GPS altitude or a flight level. They are not interchangeable.
- Use the simulator’s weather report. Obtain QNH from its active ATIS, automated weather broadcast or weather interface. A real-world report from another time or station may not match live or manually configured simulator weather.
- Set local QNH and verify the units. Confirm whether the instrument displays hectopascals or inches of mercury. Standard pressure is 1013.25 hPa, equivalent to 29.92 inHg. Microsoft Flight Simulator 2024 users can follow our practical checks for locating the BARO control, selecting units and checking multiple altimeters.
- Check QFE and STD modes. Use QFE only when a procedure specifically calls for height above the airfield. On climb, select STD when passing the local transition altitude; on descent, restore local QNH by the transition level. Transition altitude is not the same worldwide.
- Check every instrument. The pilot, co-pilot and standby altimeters may have independent controls. Changing one side of an airliner cockpit does not necessarily update the others.
- Run a controlled comparison. Park at a known airport in settled weather, disable simulated instrument failures and test a default aircraft. If every aircraft is wrong by the same amount, suspect weather or scenery; if only one aircraft is affected, suspect its instruments, saved state or custom systems.
What does the size of the altitude error reveal?
The size and behaviour of the error usually identify the cause faster than repeatedly turning the pressure knob.
A one-hectopascal pressure-setting error changes indicated altitude by roughly 27 feet near sea level; 0.01 inHg represents about 10 feet. Setting pressure too high makes the indicated altitude too high, while setting it too low makes the indication too low.
| Error pattern | Likely cause |
|---|---|
| A few tens of feet on the ground | Weather rounding, runway slope, instrument tolerance or a different charted elevation point |
| Near zero instead of airport elevation | QFE is selected where QNH was expected |
| Several hundred feet wrong | STD mode, stale QNH, pressure from another station or incorrect units |
| Correct near the airport but increasingly different aloft | Non-standard temperature or comparison with GPS or geometric altitude |
| Reading freezes during a climb or descent | Blocked static source, static icing or a simulated instrument failure |
| Wrong only at one airport or runway | Airport elevation, terrain mesh or add-on scenery conflict |
Why does GPS altitude differ from the altimeter?
GPS, map overlays and barometric instruments may use different vertical references, so they are not guaranteed to agree. A cockpit altimeter derives altitude from static pressure, while a GPS or simulator overlay may use geometric altitude referenced to mean sea level or an ellipsoid.
Temperature also matters. QNH corrects for pressure, but a barometric altimeter assumes a standard temperature profile; in unusually cold air, true altitude can be lower than indicated. A radio altimeter is different again because it reports height above the terrain directly beneath the aircraft.
Why is the altimeter still wrong after setting QNH?
A persistent error after entering the correct QNH usually points to an aircraft, control-binding, failure or scenery problem rather than the pressure report itself.
- Every aircraft and airport is affected: check pressure units, weather synchronisation, automatic barometer assistance and duplicated hardware bindings.
- Only one aircraft is affected: check its separate altimeters, instrument failures, static-source selection and saved cockpit state.
- Only one airport is affected: compare several runway positions; an airport or terrain add-on may be using a conflicting elevation.
- The setting changes by itself: an assistance feature, keyboard assignment or noisy controller axis may be operating the barometer control.
- The indication stops responding: inspect the static system rather than the pitot system. A pitot blockage affects the airspeed indicator, while a blocked static source affects the altimeter.
Do not force the altimeter to match a displayed ground elevation by winding the pressure away from a valid local QNH. That can conceal a scenery or datum mismatch and leave the indicated altitude wrong after take-off.