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Meteorology

Answer:

If the QNH is 993 hPa, the 1013 hPa pressure level lies 20 hPa below the 993

hPa pressure level, as the pressure from 1013 hPa is 20 hPa higher than the

pressure from 993 hPa.

Since 1 hPa corresponds to 30 ft, there are 20 x 30 = 600 ft from 1013 hPa to

MSL, and from MSL, there are 1000 feet up to the airport.

First, we calculate our altitude relative to

1013 hPa (1 hPa = 30 ft):

1013 hPa – 993 hPa = 20 hPa

20 hPa x 30 ft = 600 ft

1000 ft + 600 ft = 1600 ft

Example, density altitude:

Given:

1000 ft: 13ºC

MSL: 993 hPa, 15ºC

The setup looks like this:

Calculate standard atmospheric conditions (ISA)

Answer:

We have our pressure altitude from before =

1600 ft.

We remember that temperature decreases by

2ºC for every 1000 ft we climb (pressure

altitude).

So, the temperature at 1600 feet should be:

15ºC – (1.6 x 2ºC) = 11.8ºC (but it is 13ºC).

Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 240