Page 228 - PPL-engelsk 2025

Meteorology

3.3.5 Barometer, pressure and isobars

Air pressure is defined as the weight of the amount of air above an object.

A column of air with an area of 1 m² weighs 10336 kg.

3.3.5.1 Measurement of air pressure

A barometer is used to measure air pressure.

The unit in which pressure is measured is hPa

(hectoPascal). 1 hPa = 10.2 kg/m².

Pressure can also be measured in inches.

Standard Pressure MSL:

- 1013.23 hPa

- 760 mm Hg
- 29.92 inches Hg

Here is a schematic diagram of a
barometer.

The can is almost airless.

Compression or expansion causes the needle to move.

3.3.5.2 QFE, QFF, QNH

The air pressure at the reference point of an airport is called QFE. The altimeter

shows 0 feet, and the pressure can be read on the altimeter's window.

Based on the current temperature, the air pressure at sea level (MSL) can be

calculated, referred to as QFF. It is QFF (Q for Professionals) that is used by

meteorologists when drawing isobars on an analysis chart.

Had standard atmospheric values been used, it would result in QNH.

Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 228