Airspeed
speed of an aircraft relative to air
In aviation, airspeed is the speed of an aircraft relative to the air it is flying through (which itself is usually moving relative to the ground due to wind). In contrast, the ground speed is the speed of an aircraft with respect to the surface of the Earth (whether over land or presumed-stationary water). It is difficult to measure the exact airspeed of the aircraft (true airspeed), but other measures of airspeed, such as indicated airspeed and Mach number give useful information about the capabilities and limitations of airplane performance. The common measures of airspeed are:
Indicated airspeed (IAS), what is read on an airspeed gauge connected to a pitot-static system.
Calibrated airspeed (CAS), indicated airspeed adjusted for pitot system position and installation error.
True airspeed (TAS) is the actual speed the airplane is moving through the air. When combined with aircraft direction, wind speed and direction, it can be used to calculate ground speed and direction.
Equivalent airspeed (EAS) is true airspeed times root density ratio. It is a useful way of calculating aerodynamic loads and airplane performance at low speeds when the flow can be considered incompressible.
Mach number is a measure of how fast the airplane is flying relative to the speed of sound.
This brief starts where responsible research should: with the source description of “Airspeed” as speed of an aircraft relative to air. Everything that follows is an evidence route, not borrowed authority.
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The subject matters to the general reference register because the source frames it as speed of an aircraft relative to air. Its deeper value depends on whether names, dates, institutions and citations support that framing.
Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated Jul 16, 2026. The linked authority identifier is Q1197176. The Library of Congress control number is sh85002699. 1 of 1 selected statements include explicit references; 0 carry qualifiers and 0 use preferred rank.
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This entry incorporates text from “Airspeed” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.