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9.7.2 Speed designations GS, TAS, IAS and CAS

NOW IT'S PROBABLY A MESS IN YOUR HEAD - we'll summarize!

9.7.2.1 Ground Speed (GS)

The speed relative to the ground is

called Ground Speed (GS).

When we have a headwind, GS is less

than TAS, and conversely if we have a

tailwind, GS is greater than TAS.

9.7.2.2 True Air Speed (TAS)

The aircraft moves at a certain speed through the air. This speed is, as previously
mentioned, called the aircraft's speed in relation to the air or true air speed

(TAS).

9.7.2.3 Indicated Air Speed (IAS)

The aircraft's speed relative to the surrounding air is measured with an airspeed

indicator.

The speed we read on the airspeed indicator is called indicated air speed (IAS).

9.7.2.4 Calibrated Air Speed (CAS)

The airspeed indicator can be subject to various instrument errors. When you
make corrections for these, you achieve the calibrated air speed (CAS).

If CAS is corrected for altitude and temperature, you get TAS, the speed we use

for navigation.

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Flyveteori PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 848