Editing Indicated airspeed (section)

==Other airspeeds==
From IAS, the following speeds can also be calculated:
* convert CAS to [[equivalent airspeed]] (EAS) by allowing for compressibility effects (not necessary at slow speed or low altitude);  EAS is used by aircraft engineers and some very high-altitude flying aircraft such as the U-2 and the SR-71;
* convert EAS to [[true airspeed]] (TAS) by allowing for differences in [[density altitude]].

On large jet aircraft the IAS is by far the most important speed indicator.  Most aircraft speed limitations are based on IAS, as IAS closely reflects dynamic pressure. TAS is usually displayed as well, but purely for advisory information and generally not in a prominent location.

Modern jet airliners also include [[ground speed]] (GS) and [[Machmeter]]. Ground speed shows the actual speed that the aircraft uses compared to the ground. This is usually connected to a [[GPS]] or similar system. Ground speed is just a pilot aid to estimate if the flight is on time, behind or ahead of schedule. It is not used for takeoff and landing purposes, since the imperative speed for a flying aircraft always is the speed against the wind.

The Machmeter is, on subsonic aircraft, a warning indicator. Subsonic aircraft must not fly faster than a specific percentage of the speed of sound. Usually passenger airliners do not fly faster than around 85% of speed of sound, or Mach 0.85. [[Supersonic]] aircraft, like the [[Concorde]] and military fighters, use the Machmeter as the main speed instrument with the exception of take-offs and landings.

Some aircraft also have a [[taxi speed indicator]] for use on the ground. Since the IAS often starts at around {{cvt|40|-|50|kn|km/h|order=flip}} (on jet airliners), pilots may need extra help while taxiing the aircraft on the ground. Its range is around {{cvt|0|-|50|kn|km/h|order=flip}}.