What does “Unable” mean and what is it used for?

Normally if ATC tells you to do something, you do it or get reported. Is the “Unable” response basically saying “Hey ATC I want you to ghost me!”?


That was posted in 2015…

It’s also not very descriptive.

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It’s still relevant


Basically means if your plane can’t do what atc requested ex: Going down to 2000ft but the surface is 2500ft high

What if there is a TFR in effect from SFC to 18,000 MSL saying not to go there and the controller says go down to 10,000 MSL. Do you use the “Unable” command?


Yes, but I don’t think there is any TFR like that. (Excluding Size restrictions, but that’s not really needed since most of the time you fly above the TFR)

Really, it all boils down to whether you can physically carry out the instructions. If you can, then just follow them.

ATC vectoring you into a mountain? Yes, say unable.

ATC Vectoring you too close to the ground? Yes, say unable.

ATC vectoring you to the back of an approach line, but you don’t want to wait and cut in front? No, don’t say unable (unless you’d like to be ghosted).


In essence the word means exactly what it says in the dictionary.

As long as you don’t use it to mean “I do not feel like it” you are fine.

(But there are also cases where you see pilots who genuinely think they are unable but they really can. So it is a mix. Mostly this is with speeds. Generally if you ask a 388 going 250 knots on base at intercept altitude to slow, they may truely think they can’t because “Oh I’m heavy,” but they can. 388s don’t land at 250 knots, so you have to slow down some time.)


MaxSez: Mind reading now Tim? LOL…
Who’s the Judge in these “Unable” cases on IF @Tim_B? A reasonable person without a bias would side with the Pilot every time. Unable is not a judgement call it a statement of fact as the PIC assesses the situation at the time. As “The Decision Maker” the PIC has total responsibility for safe passage in Controller and Un-Controlled Airspace. Second guessing & skill set speculation by a controlling agency on the ground miles away is wrong headed in these cases. Bottom line; “Unable” is legal terminology and is purpose driven. It is not a dirty word or an attempt to get over, don’t rationalize, accept it and the fact that the PIC has the Dot. Who lov’s ya baby, Regards, Max Sends
(Just Lov those oxy’morons)

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That would have been totally necessary for a blog post as well as a PM.

Well, let’s just say it’s not borderline. 200 vs 190? Sure.

But you can’t tell me that there is a commercial airliner on this world that hits a 10 mile final at 250 KIAS as a minimum possible speed.

(Regarding the other ones, yes, PIC and all that. Well aware.)


I’m in total agreement with you 99% of the time @Tim_B. Off times you express your bias and valid observation in your extemporaneous comments included with your valid technical/procedure teaching points which give me pause. Thus the snotty retort to get your attention when
your example miss the mark in my opinion.
The “speed example” does not fit smartly into an “Unable” notch…
All comers on the ES “must” know Controlled Airspace has a speed limit, a nugget/malcontents “Unable” retort in Overspeed intro that space deserves; a go downwind, a vector to nowhere, a 360 or Ghost …Learning experiences. Take no prisoners is the proper corrective learning moment here… Just sayin, Have a nice day,
Warm Regards my “Expert Mentor”, Ron


What do you think of “maintain best forward speed” command on short final?

Happened to me last week when the pilot behind me didn’t maintain separation. I WAS on my best forward speed for the situation - which is of course slow when you’re on short final.

I was threatened to be ghosted and had to quit immediately.

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That’s a controller issue. Message one of us if you’re unsure.

Reasonable speed while on short final is not something that should be modified at the controller’s will. It’s a critical phase of flight.


Today, a radar controller told me to descend to 8000 and fly no more than 200kts and my plane almost stalled out, I’d hate to say unable as it was very busy and I didn’t want to stress him out, but I must say, I had my flaps out for like an hour trying not to stall.


urm airspeed not ground speed… so you shouldnt have stalled out

I don’t think you saw what happened

stalling with 200kts in an a321, was there an space shuttle on top?


Speed commands shouldn’t be issued on short final.

In that case, a go around should be used if needed to avoid any conflicts.

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