Speed difference ???

[scanhorse]

Hi
I surpose the speed on map is a calculated speed, or ?
or is it transmitted by A/C ?
I hear pilots say speed 250 and map shows over 300
or is it the difference between air-speed and ground-speed ?

Ulf Scanhorse

[Mike]

Speed comes from transponder, but there are many different speeds in aviation. IAS (indicated airspeed), TAS (true airspeed), CAS (calibrated airspeed), GS (ground speed).

http://en.wikipedia.org/wiki/Indicated_airspeed

I think that transponder speed is GS.

[andy1]

i heard also stable flight level 150 the speed is 280knts and on the map i read 350 ?

what speed shown on the map ?

[fungus]

i heard also stable flight level 150 the speed is 280knts and on the map i read 350 ?

what speed shown on the map ?

Air Traffic Control (ATC) use Indicated Air Speed (IAS) and from memory the map shows ground speed so if you 'heard' a speed reference then I'm assuming you mean via ATC so this may explain the difference. Here in Australia aircraft are speed limited to 250Knts (IAS) below 10,000ft (the transition altitude and obviously I'm refering to aircraft capable of these speeds) when flying in controlled airspace unless authorised to ignore this limit by ATC but you'll notice the speed on our radars (and the map) is greater than that set by the pilots/or requested by ATC.
Regards,
Gregg

[jakob]

Basically:

IAS - the speed from the airspeed indicator. This is the speed air traffic control and pilots use when communicating. Also, this is the speed that is used in airspace/airport limitations and regulations, at least in Europe (e.g. 250 kt below 10,000 ft or 160 kt until OM).
TAS - the actual speed that the airplane is moving through the air (IAS with applied corrections for air pressure/temperature). Will be much higher than IAS at high flight levels, (~300kt IAS on FL350 is ~500kt TAS).
GS - the speed that the airplane is flying relative to the ground. (TAS with applied corrections for headwind/tailwind). This is the speed that is shown on Flightradar24.

For example, if a plane is flying with speed 220 kt IAS at 7000 ft, its TAS will be ~245 kt. Let's say it has 20 kt tailwind, then the GS (and thus what FR24 display) will be 265 kt.

[Jarod]

A lot of times i hear ATC ask: KLM 898 speed 220, and then the plane responds with: "Already at 220, KLM 898."

Funny how that works.