Quick Facts
- Type
- Instrument Parameter
- Definition
- The barometric pressure value set on an aircraft's altimeter so that it reads...
- Used By
- Pilots, ATC
Definition#
The altimeter setting (QNH in ICAO terminology) is the barometric pressure adjusted to sea level, used to calibrate an aircraft's altimeter so it displays the correct altitude above mean sea level (MSL). In the U.S., it is expressed in inches of mercury (inHg).
Why It Matters Operationally#
An incorrect altimeter setting causes the altimeter to read incorrectly, potentially placing the aircraft at a different altitude than indicated. METARs include the current altimeter setting (A-group), and ATC provides updates.
Related Guides#
- How to Read a METAR
- Density Altitude Explained
- Aviation Weather Explained — The Complete Operational Guide