Page 243 - PPL-engelsk 2025
P. 243
Meteorology
The importance of setting the altimeter correctly is shown in the diagrams
below, which illustrate indicated and true altitude when flying into areas with
lower pressure or temperature.
In the scenario shown, the following conditions are met:
- Altimeter height: 1000 ft
- True height: 1000 ft
- Temperature: 13ºC
- QNH: 1023
flying into lower pressure with
the following conditions:
- Altimeter height: 1000 ft
- True height: 400 ft
- Temperature: 14ºC
- QNH: 1003
We can see that with a decrease in QNH from 1023 to 1003, the true altitude
drops from 1000 ft to 400 ft, whereas the altimeter still shows 1000 ft. This can
obviously have catastrophic consequences if flying on instruments. Had we
flown into higher pressure, the opposite would have been the case.
In this case, the following conditions apply:
- Altimeter height: 1000 ft
- True height: 1000 ft
- Temperature: 13ºC
- QNH: 1013
flying into lower temperature with
the following conditions:
- Altimeter height: 1000 ft
- True height: 900 ft
- Temperature: -12ºC
- QNH: 1013
Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 243
