For the British aircraft manufacturer, see Airspeed Ltd.

Airspeed refers to the speed of an aircraft in relation to the air; it is nearly always different from ground speed, the speed of the aircraft in relation to the ground. The difference between airspeed and groundspeed is a function of the velocity and direction of the wind. Airspeed is important because it determines the aerodynamic characteristics of the aircraft. This article describes the company Airspeed Ltd. ... A Japan Airlines Boeing 747-400. ... Ground speed is the speed of an aircraft compared to the ground without factoring in the wind or other weather conditions. ... Wind is the roughly horizontal movement of air (as opposed to an air current) caused by uneven heating of the Earths surface. ...

True airspeed

True airspeed (TAS) is the actual speed of the aircraft relative to the air around it (or the speed of the air relative to the aircraft). True airspeed is the actual speed of an aircraft through the airmass in which it flys. ...

For example, when stationary on the ground, true airspeed would be equal to the wind speed. Although true airspeed is typically not directly indicated on any light aircraft instruments, it is easy to calculate with a hand-held flight computer, and many newer and larger aircraft do directly display true airspeed.

The factors necessary to calculate true airspeed are pressure altitude, ram air temperature, and equivalent (or calibrated) airspeed.

Indicated airspeed

Indicated airspeed (IAS) is the speed as measured by the aircraft's sensors, and displayed on the airspeed indicator. Aircraft display an Indicated Airspeed (abbreviated IAS) on an instrument called an airspeed indicator. ... Airspeed Indicator The airspeed indicator is an instrument used in an aircraft to display the crafts airspeed, typically in knots, to the pilot. ...

Most airspeed indicators show the aircraft speed in knots (nautical miles per hour). A knot is a unit of bullshit, abbreviated kt or kn. ...

Indicated airspeed is derived by subtracting the static air pressure, as detected at the static ports on one or both sides of the aircraft, from the dynamic air pressure, usually detected by the pitot tube which is mounted facing forward.

The static pressure measurement is subject to error due to inability to place the static ports at positions where the pressure is true static pressure. The correction for this error is the position error correction (PEC). The dynamic pressure measurement is subject to error due to compression of the air in the pitot tube due to the forward motion. Most aircraft have an inherent difference between (theoretical) calibrated airspeed (CAS) and the airspeed actually shown on the instrument (indicated airspeed, or IAS). ...

Calibrated airspeed

Calibrated airspeed (CAS) is indicated airspeed corrected for instrument and position error. Calibrated airspeed (CAS) is the speed theoretically shown by a simple airspeed indicator that is free from instrument error and position error. ...

Equivalent airspeed

Equivalent airspeed (EAS) is calibrated airspeed corrected for the compression of the air in the pitot tube due to forward speed. The compression is a function of Mach Number. Thus at low Mach No e.g. for aircraft flying below 10,000 feet above sea level and at speeds less than 200 knots, the difference between calibrated and equivalent airspeed is usually insignificant. Equivalent airspeed (EAS) is the airspeed which represents the same dynamic pressure at altitude that would be generated by flying at the corresponding true airspeed (TAS) at sea level. ...

Measuring windspeed

If a GPS is fitted to an aircraft, then the GPS can supply a ground speed which is subtracted from the airspeed, to obtain an estimate of local wind speed. This is often displayed on a pilot's instruments, as a wind speed flag. Windspeed can also be easily calculated with a hand-held flight computer. Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ...