When should pilots reset the altimeter setting?

Pilots reset the altimeter whenever the applicable pressure reference changes: before take-off, after receiving a revised local setting while flying by altitude, climbing through the transition altitude to standard pressure, and descending through the transition level back to local pressure. Exact changeover points come from regional rules, charts, ATC and operator procedures.

In real-world aviation and realistic flight simulation, resetting the altimeter means changing its barometric reference—not zeroing or recalibrating the instrument. Our explanation of QNH and standard pressure covers what those pressure references represent.

When is each altimeter change made?

Some regions or operations use QFE, which makes the altimeter read approximately zero at a specified datum. Pilots use it only when the procedure explicitly calls for it; QFE must not be substituted for QNH by habit.

When do pilots switch between QNH and standard pressure?

Pilots normally select standard pressure while climbing through the published transition altitude, then restore local pressure while descending through the applicable transition level. These are not necessarily the same height because a transition layer separates altitude-based traffic from flight-level traffic.

The transition altitude may be fixed nationally, published for an aerodrome or specified on a procedure. The transition level can vary with atmospheric pressure and may be issued by ATC or included in arrival information. Our guide to finding operational information on aviation charts explains where to look for these details.

In much US-controlled airspace, the change to 29.92 inHg is associated with 18,000 feet, but pilots must not assume that rule applies worldwide. Many countries use much lower transition altitudes.

During descent, crews may enter destination QNH into an approach or performance page before reaching the changeover point. That does not necessarily change the pressure reference shown on the primary flight display. The actual altimeter must still be switched at the correct stage; our 737 descent and approach sequence shows where that action fits into cockpit preparation.

Should pilots change the setting whenever ATC gives new pressure?

Pilots flying by altitude should set a newly issued local pressure promptly and confirm it as required. A pressure change alters the indicated altitude even though the aircraft has not physically climbed or descended.

An aircraft cruising at a flight level remains on standard pressure, even if ATC broadcasts a new surface altimeter setting. The new QNH becomes relevant when the aircraft descends back into altitude-based operations.

The risk is greatest when flying from an area of high pressure towards lower pressure without updating the setting: the aircraft is lower than the indicated altitude. Below the transition altitude, pilots therefore keep the setting appropriate to their route rather than retaining a stale departure value.

How should an altimeter reset be checked?

1. Identify the correct reference. Obtain the pressure from ATC, ATIS or another approved source and verify whether the flight should be using altitude or flight level.
2. Check the units. Confirm whether the instrument is displaying hectopascals or inches of mercury. Standard pressure is approximately 1013 hPa or 29.92 inHg.
3. Set every required instrument. Update both pilots' altimeters where fitted, plus the standby altimeter. Do not assume that changing one display automatically synchronises the others.
4. Verify the indication. Check for the expected QNH or STD annunciation and a plausible altitude change. One hectopascal represents roughly 27 feet; 0.01 inHg is about 10 feet.
5. Cross-check the flight mode. Ensure clearances, selected altitude and call-outs now use altitudes or flight levels consistently with the pressure reference.

Which altimeter-setting mistakes cause problems?

• Switching at 10,000 feet automatically, even though the published transition altitude is different.
• Selecting destination QNH as soon as descent begins while the aircraft is still cleared at a flight level.
• Changing the captain's display but leaving the other primary or standby altimeter on the old setting.
• Entering 1013 when the instrument is using inHg, or misreading a setting such as 29.92.
• Leaving the departure QNH set after entering an area with substantially different pressure.
• Confusing QNH with QFE and consequently introducing an aerodrome-elevation error.
• Trying to compensate for cold temperature by turning the pressure-setting knob. Required temperature corrections are applied to relevant procedure altitudes; they do not replace the reported QNH.

Does the procedure change in a flight simulator?

The pressure-setting logic is the same in a simulator, but the weather source matters. Use the pressure reported by the simulator's active ATIS or ATC system when that is what controls the simulated environment; an external report may describe different weather.

An automatic “set altimeter” command may select local pressure even when the aircraft should remain on standard pressure at a flight level. Treat it as a convenience rather than a substitute for the transition procedure. For the cockpit controls and weather sources in Microsoft's newer simulator, see our practical MSFS 2024 QNH procedure.