"Unable" Message

Hello IFC! I have a few questions about the “unable” message. I’ve seen people use it just because they don’t want to follow ATC instructions, and how does ATC tell the difference from a legitimate use or a fake one? Can you get reported for using the “unable” message? And lastly, in what circumstances would you reply “unable” to ATC. Any help is appreciated!

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Well lots of people on expert accidentally reply with unable so you should here im sorry after and if not then they probably dont want to listen to ATC

Yes you can for not following inturctions unless you reply with Im Sorry and continue what what ATC told you

Unless your heading for a mountain

Hope this helps!

And correct me if I said anything wrong


Adding on, you can reply with “Unable” for either terrain or if APPR requests you to maintain a speed you cannot fly with like 120 knots in an A320


It’s a mix of both situational awareness and the knowledge of the airspace around the airport. As an approach controller, I never open a facility before looking at the terrain on ifatc.org and examining the different STARs (with their altitudes on waypoints) which means that when I open a station I already know what to expect and can predict if the “Unable” reply is false.

If an aircraft does send an “Unable” message I check that I didn’t put them on a course with any terrain or aircraft/and that I didn’t request something of them that a reasonable pilot cannot accomplish. If I didn’t, then the “Unable” command is bogus and I send a “Please follow instructions” command which usually prompts the aircraft to follow my instructions.

99.99% of the time I get an “Unable” reply is when the aircraft can see that they’re going to be entering a rather long hold, especially at a hub airport. As mentioned previously, a simple “Please follow instructions” usually solves the issue.

If you have any more questions feel free to ask :)


As a pilot, the only time I’ve ever truly needed to use “unable” were during times I may have been given vectors from ATC that were physically impossible.
One example, was I was in a caravan, and was told to maintain a speed that I physically was incapable to maintaining. Thus, I was obligated to use “Unable”
Another example, was when I was flying in an area with a ton of terrain, and the controller accidentally vectored me too low to terrain. Therefore, I used “unable”

As from an IFATC point of view, “unable” is typically used when an aircraft requests a runway change. Although we do everything we can to accommodate runway change requests, sometimes it just isn’t possible given traffic, terrain, or airport layout.


Thanks everyone for the help!

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