Page 770 - PPL-engelsk 2025

Aircraft general knowledge

8.12.5.2 Speed designations

There are different designations for speed:

- Indicated air speed, IAS, is what is read on the instrument.

- Calibrated airspeed, CAS, is the indicated airspeed corrected for instrument

error and position error on the pitot tube (at high angles of attack).

On newer airspeed indicators, CAS = IAS

- The true air speed, TAS, (True Air Speed) changes with altitude, as the air
becomes thinner the higher we go, the airspeed indicator will show too little.

This can be corrected by 2% per 1000 feet or according to the table.

8.12.5.3 Instrument error

At low speeds, position errors can occur due to the position of the pitot tube

with the high angle of incidence.

Simulator showing the pitot-static system

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8.12.6 Altimeter

You can say that the altimeter is in reality just a barometer, where instead of

pressure in hPa or millibar, the unit of feet are set on the scale.

Since 1 hPa is approximately 30

feet, this means that for every
30 feet you move up in the air,

the pressure drops by 1 hPa.

Here you can see a schematic

diagram of the altimeter.

Flyveteori PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 770