Setting QNH Correctly for Descent and Approach on Airbus
Barometric pressure setting sounds like a small checklist item, yet it is one of the most common reasons an otherwise perfect NG ROUTE-planned ILS approach falls apart in the simulator. Airbus aircraft make QNH especially visible because the FMGC, FCU, and PFD altitude bugs all assume the altimeter reference you selected is correct. If you still have STD (1013 hPa) on the FCU while descending into an airport at 1018 hPa, your indicated altitude will be wrong by hundreds of feet — the glideslope intercept will look broken, the bird will not match the runway, and autoland may disconnect.
Transition altitude and transition level
Climbing out, you pass transition altitude and set STD on the side windows and FCU. Descending in, you must return to local QNH at the published transition level or when ATC clears you to QNH — whichever your procedure says first. In Europe this is often FL70 or FL60; in the US procedures differ. NG ROUTE arrival METAR shows the destination QNH directly in the weather card — copy that number before top of descent.
Where to set QNH on Airbus
- FCU BARO knobs — both sides for consistency in training
- EFIS — confirm BARO displays hPa or inHg per unit preference
- MCDU PERF APPR — some fleets enter QNH for approach baro minimums and radio altimeter logic
- Standby altimeter — set to QNH as cross-check
In the sim, set QNH at the same callout you would use on a line flight: typically “QNH set” passing transition level or when leaving cruise descent clearance.
What goes wrong if you forget
Suppose the true destination QNH is 1020 hPa but you remain on 1013. Altimeter reads roughly 70 feet higher than true altitude (rule of thumb near 30 ft per hPa in lower atmosphere). The aircraft flies physically lower than indicated. On ILS, you may dip below the glideslope beam while PFD suggests you are on path — GS flashes, autopilot pitches up abruptly, or you land short. On a non-precision approach, MDA becomes meaningless because you are comparing a false altitude against a true ground obstacle clearance.
Autothrust and APPR mode may also inhibit because baro and radio altimeter consistency checks fail in advanced add-ons.
Pairing with NG ROUTE briefing
When you build a route, note arrival METAR QNH alongside suggested runway. If using live weather in MSFS or X-Plane, the sim atmosphere should match; still set the FCU manually because some aircraft never sync baro from sim weather automatically. For Aerofly, procedures may stay on 1013 per NG ROUTE guide — know your platform.
Recommended call flow in the sim
- At T/D or descent briefing: read METAR QNH from NG ROUTE
- Passing transition level: PF sets BARO, PM cross-checks standby
- Approach briefing: confirm QNH unchanged if METAR updated (SPECI)
- 500 ft stable check: altimeters match and agree with tower ATIS
Memory aids
If altitude callouts on final do not match what you see out the window, suspect QNH first before blaming the ILS station. A quick BARO correction is cheaper than a go-around from a dive — but if below 1,000 ft with large error, go around and reset.
Correct QNH is the bridge between NG ROUTE weather briefing and a trustworthy Airbus approach. Set it once, verify twice, then trust your glideslope.
Altimeter and transition procedures vary by state and operator. Real-world flights use only approved charts and SOPs.