True airspeed (TAS) is the speed of an aircraft relative to the airmass in which it flies, i.e. the magnitude of the vector difference of the velocity of the aircraft and the velocity of the air. Under zero wind conditions this is equal to the speed over the ground. Under wind conditions an estimation of the wind is used to make a windspeed vector calculation that computes an estimated ground speed from the true air speed and a wind correction angle to maintain the desired ground track.

Aircraft display an indicated airspeed on an instrument called an airspeed indicator. Indicated airspeed will differ from true airspeed at air densities other than some reference density. Air density is affected by temperature, moisture content, and altitude. Indicated airspeed is used in aircraft operation as the aircraft stalling speed and structural limiting speeds are dependant on indicated airspeed, irespective of true airspeed. However, proper navigation via dead reckoning (without constant ground reference) requires the use of true airspeed and wind corrections. 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. ... Dead reckoning is the process of estimating a global position of a vehicle by advancing a known position using course, speed, time and distance to be traveled. ...

TAS can be calculated as a function of Mach number and static air temperature, or as a function of Mach number and total air temperature. Mach number (Ma) (pronounced mack in British English and mock in American English) is defined as a ratio of the speed of an object or flow relative to the speed of sound in the medium through which it is travelling. ... This article lacks information on the importance of the subject matter. ...

where

TAS = true airspeed in knots
M_a = Mach number
T_static = static air temperature in degrees Celsius
T_total = total air temperature in degrees Celsius

Electronic flight information systems (EFIS) contain an air data computer with inputs of total air temperature, impact (pitot) pressure and static pressure. Since Mach number is a function of impact and static pressures, an EFIS can compute and display TAS. An air data computer is an essential avionics component found in modern glass cockpits. ...

In simple aircraft, without an air data computer or Mach meter, true airspeed can be calculated as a function of equivalent airspeed and local air density (or static air temperature and pressure altitude which determine density). Some airspeed indicators incorporate a slide rule mechanism to perform this calculation. Otherwise, it can be performed with a calculator such as the E6B handheld circular slide rule. 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. ... The slide rule, or slipstick, is an analog computer, usually consisting of three interlocking calibrated strips and a sliding window, called the cursor. ... The front of a metal E6B. An E6B flight computer commonly used by student pilots. ... The slide rule, or slipstick, is an analog computer, usually consisting of three interlocking calibrated strips and a sliding window, called the cursor. ...

See also

• Flight planning

Flight plans are plans filed by pilots with the local regulatory authority (e. ...

References

(1 December 1989) Air Navigation, Department of the Air Force. AFM 51-40.