During a flight yesterday, the approach frequency for a local Class C was unusually busy. I was heading back to an underlying Class D and the frequency finally quieted down enough for me to poke in a call of Huntsville Approach, Cessna 123AB, VFR with request.

ATC responded with <identifier>, remain VFR. I am not positive whether he gave the full callsign or just Tree Alpha Bravo — either way, definitely not Aircraft calling. He did not instruct me to remain clear.

I understand that radar advisories are workload permitting for VFR traffic, and clearly ATC had all the workload they could handle. Does that reply establish two-way radio communication and thus permit entry into their Class C airspace, just without flight following? What if the reply had been Tree Alpha Bravo, remain VFR? Assuming it does establish two-way communication, is it good Aeronautical Decision Making to fly into known busy airspace without advisories?

Rather than requesting confirmation on a busy frequency, I descended below the shelf feeling like a scud runner. Approach and landing at the Class D were otherwise uneventful.

  • $\begingroup$ Their workload may have nothing to do with the class c airspace busyness. Remember that an ATC facility can control more (a lot more in some cases) air than is typically charted on a sectional; they could be working 5 IFR students at a satellite airport and be unable flight following. $\endgroup$ – egid Jul 27 '15 at 2:07

Yes, you were allowed to enter the class C in that case, but you weren't cleared to do it because no clearance is needed to operate in class C, just communication with ATC. The AIM 3-2-4 has the best explanation of this (see also the basic regulation in 14 CFR 91.130):

  1. If the controller responds to a radio call with, “(air craft callsign) standby,” radio communications have been established and the pilot can enter the Class C airspace.
  2. If workload or traffic conditions prevent immediate provision of Class C services, the controller will inform the pilot to remain outside the Class C airspace until conditions permit the services to be provided.
  3. It is important to understand that if the controller responds to the initial radio call without using the aircraft identification, radio communications have not been established and the pilot may not enter the Class C airspace.

So if the controller used your callsign then you've established radio communications and you can enter. This also applies to class D but not to class B, where you need an actual clearance to enter. (This is a classic exam question/scenario, by the way.) As @rbp suggested, the instruction to "maintain VFR" was probably the controller's way of letting you know up front that he was too busy to give you a pop-up IFR clearance or whatever else you might have wanted. (Maintain is an official ATC term, remain is not, although the controller may still have used it accidentally.)

As for flying into busy airspace, it's up to you as PIC to determine what's safe and what isn't. If you had the HSV ATIS (so you can anticipate traffic patterns), were squawking 1200, were in communication with ATC and were keeping your eyes outside the cockpit then there's not too much more you can do (you could turn on all your lights if you think you need to make yourself more visible). But, if you ever feel unsafe or uncomfortable in any flight situation then you shouldn't hesitate to take action - like staying clear of the class C for a few minutes - if you do feel it's necessary, that's simply part of gaining ADM experience.


You have to differentiate between a clearance which has a specific regulatory definition that is covered by numerous FARs, and the regulation which requires you to establish 2-way communication before operating in Class C or Class D. If you hear your numbers, you have established 2-way communication, and that's it. Its not a clearance, as defined by the FARs.

"Remain VFR" is completely different instruction not related to permission to operate inside the Class C. It is usually given when the controller thinks you might be calling him up to request an IFR or SVFR clearance and he is telling you, in advance, that he can't do it right now.

It is also unfortunate that "remain clear" and "clearance/cleared" both use the same word. But they mean completely different things. "remain clear" has nothing to do with a clearance, but tells you to remain outside the controller's airspace.

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    $\begingroup$ Note that, at least in the US, the official phraseology is "Remain Outside". "Remain Clear" is not standard phraseology, though it sounds like you've heard it before. $\endgroup$ – NathanG May 24 '15 at 1:35

No clearance is required for VFR Flight in Class C airspace. It is however required to establish two way radio communications (FAR 91.130). The most common interpretation I've come across is that as long as ATC have responded with your callsign, you have established two way radio communications, and are therefore free to enter, unless instructed to remain clear.

I'll leave the discussion about ADM to others, but being unsure of what the ATC response meant, you took the conservative route, based on the information in your post. However, even if ATC is busy, it is very seldom too much to ask for clarification.

  • $\begingroup$ that last part is superfluous for Class C and D. if you hear your numbers, you've established 2-way communication, and that is all thats' required. A non-establishment radio call will sound like "Aircraft calling San Jose, remain clear" or "Aircraft calling, standby" $\endgroup$ – rbp May 23 '15 at 13:31
  • $\begingroup$ @rbp, technically, I agree, but not for the purpose of clearing out any ambiguities, either due to poor reception, interference, or a vague response. The exchange Greg had is however pretty standard. $\endgroup$ – Waked May 23 '15 at 13:36
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    $\begingroup$ Since its not a clearance, you are not obligated under 91.123 to request clarification. I repeat its not a clearance, "confirm clear" doesn't make any sense $\endgroup$ – rbp May 23 '15 at 13:38
  • $\begingroup$ You are however per 91.123b obligated in controlled airspace not to operate in contrary to ATC instructions. For this purpose, if you did not understand ATCs last transmission, it would be prudent to ask for clarification. $\endgroup$ – Waked May 23 '15 at 14:02
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    $\begingroup$ This is not an issue of ambiguity in the controller's transmission -- this is a clear case of @greg bacon not understanding the regulations. Also, 91.123 says When a pilot is uncertain of an ATC clearance, that pilot shall immediately request clarification from ATC. That's not an instruction. There is no obligation to clarify an instruction, although its prudent. $\endgroup$ – rbp May 23 '15 at 14:10

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