ATC Speed Commands Are Transmitted in Ground Speed and not IAS

My speed is as follows: 214knts GS, 191knts IAS

When given the speed command, I was told to reduce speed to 200knts IAS, I’m already below 200knts IAS.

Therefore I believe that when an approach controller gives a speed command, the use of the word decrease or increase seems to be determined by the aircraft’s Ground Speed and not IAS.

iPhone 6s
iOS 12.1

No we are telling them IAS not ground speed.

I know, as a pilot you receive it in GS.

As far as the speed up slow down?

That’s what made me assume it was transmitted in ground speed.

I got ya now yea that’s always annoyed me.

Same, always wondered why.


Pilot speed shows in GS while ATC transmit in IAS.
That got me in trouble but that’s not an issue I believe.

ATC send speed commands in IAS, we have a menu to select certain speeds. When the pilot receives the command from what I gathered, it is being sent in ground speed when it’s supposed to be sent in IAS. This can be confusing as you can imagine.

For context regarding what you’re talking about by getting in trouble, the speed shown on the radar as a controller has been and still is in ground speed so that’s unrelated. Ground speed and IAS generally displays similar speeds (realitively speaking), so I would have never noticed it if I didn’t have a headwind.

Actually nothing tell us it’s being send in IAS, maybe people near to the dev team or IFATC could help us figure it out.

I’m IFATC. 🙂

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Then maybe they changed it in last update who knows, I haven’t been in controlled airspace since then.

But I’m curious so I’ll see the answer you get to this topic

The answer to the topic is what Trio is reporting is the incorrect function of the speed command as far as increase or decrease speed. Trio is on point that the instruction is given in IAS as it is in the real world. The Increase and Decrease just needs to be removed from the wording.


Ok I get the “increase” and “decrease” part.

But isn’t that logic that ATC transmit in GS since they only know pilot’s GS?

Would it require ATC to know our IAS ? (Yes I guess)

We make educated guesses based off the wind. Being able to see the ground speed on radar as a controller is important in my opinion. If one aircraft has a 40knt tailwind and the other has a 40knt headwind and we can only see IAS then we wouldn’t know why the one aircraft is moving faster then the other. That kind of guessing would be much more annoying then having to guess aircraft’s IAS for speed commands. 🙂


Yes, GS is more useful in these case

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