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What ceiling does the FAA consider to be controlling for FAR 91.155(c)? The ceiling reported at the airport for which the surface-level controlled airspace is designated, or the ceiling directly above the airplane?

What specific guidance has the FAA issued on this topic?

FAR 91.155(c) prohibits VFR flight (in the absence of a Special VFR clearance) "beneath the ceiling under VFR within the lateral boundaries of controlled airspace designated to the surface for an airport when the ceiling is less than 1,000 feet."

Note that in some cases surface-level controlled airspace extends more than 25 miles from the airport for which the airspace is designated.

Just for clarity, let me emphasize that this isn't meant to be a question about the status of "extensions" in relation to FAR 91.155(c), so maybe SIT/PASI (linked above) is a somewhat ambiguous case-- I just picked it because the surface-level controlled airspace extends so far from the airport. KSHR in Sheridan WY is another case with rather expansive surface-level controlled airspace, that avoids the "extension" issue.

Or to "put a finer point on it":

  1. If the airport (for which the surface-level controlled airspace is designated) is reporting a 900' ceiling, does that mean I can't operate VFR (without a Special VFR clearance) below any cloud ceiling, regardless of its altitude, anywhere in the surface-level controlled airspace? Or if I deem that the ceiling in a distant portion of the surface-level controlled airspace is clearly above 1000' AGL, am I fine to operate under VFR in that portion of the airspace, below the ceiling, without a Special VFR clearance, so long as I stay 500' below the clouds and meet the other rules applicable to flight in Class E airspace?

  2. Same as 1), but I'm operating in a distant portion of the airspace where there is no cloud ceiling at all. Do I still need a SVFR clearance?

  3. Conversely, if the airport (for which the surface-level controlled airspace is designated) is reporting a 2000' ceiling, but my flight path will take me over high terrain where the ceiling appears to be lower than 1000' AGL, am I ok to operate under VFR without a Special VFR clearance, as long as I can stay 500' below the clouds and meet the other rules applicable to flight in Class E airspace?

  4. If the reported ceiling at the airport is considered to be the controlling factor for FAR 91.155(c), and automatically causes the entire surface-level controlled airspace to be considered "IMC" (i.e. off limits to VFR traffic without a Special VFR clearance) up to some level, even if flying in a distant portion of that airspace where there are no clouds, then what defines the top of that off-limits ("IMC") airspace? Does the top of that off-limits ("IMC") airspace have a constant AGL height, equal to the reported cloud ceiling at the airport? Or does it have a constant MSL height, equal to the MSL equivalent of the (AGL) ceiling reported at the airport?

Another way to think about the question, is to ask "when flying VFR without a Special VFR clearance, if I'm only going to be operating in a distant portion of the surface-level controlled airspace, in what circumstances am I obligated to determine the reported cloud ceiling at the airport for which the airspace is designated, via listening to the radio or other means? Any time I think there may be a ceiling 1000' or lower over the airport? Or only in cases where that information would help me ensure that I don't fly below a ceiling lower than 1000' AGL at my location?"

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  • $\begingroup$ interesting question. In my opinion it would be the "reported" ceiling and not a pilot measured ceiling. The definition of a ceiling uses the word "reported as “broken”, “overcast”, or “obscuration”, and not classified as “thin” or “partial”. $\endgroup$
    – user22445
    Feb 21 at 15:49
  • $\begingroup$ But isn’t “the ceiling directly above the airplane” also known as cloud clearance? (is there any definition of ceiling that uses the aircraft as a reference base?!) And if the pilot is maintaining 500’ AGL or above, the weather would actually be 1500’ or better, which is VMC, which kinda renders the question moot, right? I think you can back into the correct answer here without a lot of mental gymnastics... $\endgroup$
    – Michael Hall
    Feb 21 at 19:11
  • $\begingroup$ @MichaelHall -- I wasn't meaning to suggest measuring from the airplane up to the cloud base, it's just a question about the height of the ceiling above the ground being irregular (perhaps because ground is irregular, or because cloud is limited in extent, etc...) $\endgroup$
    – quiet flyer
    Feb 22 at 14:33
  • $\begingroup$ There are some related questions, but most seem to be specifically asking about the "extension" issue which I'm really not trying to get back into right now. $\endgroup$
    – quiet flyer
    Feb 22 at 14:41
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    $\begingroup$ In my opinion, since the regulation uses the term "the ceiling" as opposed to "a ceiling" and the FAA definition of "ceiling" is a "reported" value (not a pilot measured value - see my comment above for a link to the definition of ceiling) the officially reported ceiling value applies. "Ceiling" is not a single cloud above the aircraft, it's a specific amount (% of the sky) of cloud cover classified as broken or overcast, etc., by official sources (wx observer, AWOS, etc). Just my opinion. $\endgroup$
    – user22445
    Feb 22 at 14:49

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The FAA states that a Ceiling "means the height above the earth's surface of the lowest layer of clouds or obscuring phenomena that is reported as “broken”, “overcast”, or “obscuration”, and not classified as “thin” or “partial”. A broken level is defined by the National Weather Service as "A layer of the atmosphere with 5/8 to 7/8 sky cover (cloud cover)."

(emphasis is mine)

This means that 4/8ths of the sky can be clear and the ceiling would be reported as broken. (see the image below of a ceiling)

14 CFR Part 91.155(c) states:

(c) Except as provided in § 91.157, no person may operate an aircraft beneath the ceiling under VFR within the lateral boundaries of controlled airspace designated to the surface for an airport when the ceiling is less than 1,000 feet.

(emphasis is mine)

In my opinion, this means that when the official ceiling is reported (in a METAR, for example) as "broken" (for example) this would apply to all airspace below the reported ceiling value within the entire "...lateral boundaries of the controlled airspace designated to the surface for an airport..." (ref: 14 CFR Part 91.155 (c)).

Also, in my opinion, the official ceiling reported in a METAR, for example, is not a cloud or group of clouds directly above the aircraft measured and defined as a ceiling by the pilot. Instead, it is a defined and regulatory based atmospheric condition that, if it is reported as being below 1000 ft. AGL, renders the entire surface area of the controlled airspace below that reported ceiling as IMC.

So, although some surface areas of controlled airspace surrounding an airport may be large, 14 CFR Part 91.155(c), and the definition of a ceiling, do not make any distinction or allowance for relief just because there is no cloud cover directly above the aircraft.

Image of a "Broken" ceiling (highlighting is mine). Source:

enter image description here

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  • $\begingroup$ Are the "altitudes" actually defined as semicircles like that? $\endgroup$
    – Someone
    Feb 24 at 22:51
  • $\begingroup$ @Someone I think the image above is just showing, as an example, that the ceiling is 4000 ft. AGL. The author could have eliminated 3 of the semicircles and only shown the single semicircle at 4000 ft. $\endgroup$
    – user22445
    Feb 24 at 22:55
  • $\begingroup$ So if you're in the middle of a circular field with a 4,000 foot radius, and it's foggy on the ground at the very edge, that counts as clouds at 4,000 ft? $\endgroup$
    – Someone
    Feb 24 at 22:57
  • $\begingroup$ @Someone I believe the image is just trying to depict that the observation of the cloud layer is from horizon to horizon (divided by 8ths). It could also be depicted, perhaps, as a straight line from end-to-end and defined, in this example as 4000 ft. agl. $\endgroup$
    – user22445
    Feb 24 at 23:13
  • $\begingroup$ The "octal" thing is interesting -- often when clouds are towering, there will be large areas of blue sky visible in the spaces between cloud, when looking mostly upwards, but when looking mostly horizontally all you see is the sides of more clouds-- a satellite looking down might see way less than 5/8 coverage, but... $\endgroup$
    – quiet flyer
    Feb 25 at 13:46
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The language talks about operating "beneath the ceiling ... when the ceiling is less than 1,000'." If you're not beneath that sub-1,000' ceiling, then this language doesn't apply to you.

In your point 2, if there's no ceiling where you are, then you definitely aren't operating "beneath the ceiling."

Your point 1 sounds like the cloud layer is sloping up as you get farther from the airport, and the pilot knows (how?) that where he is, there is now more than 1,000' between the ground and the clouds, while your point 3 has the ground sloping up so that the space between the ground and the clouds has become less than 1,000' where the pilot is operating. Those points would boil down to asking if the definition of ceiling,

Ceiling means the height above the earth's surface of the lowest layer of clouds or obscuring phenomena that is reported as broken, overcast, or obscuration, and not classified as thin or partial.

is related to the (clouds & earth's surface at the airport itself), or the (clouds & earth's surface where you're operating). I'll leave that distinction for a separate answer.

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  • $\begingroup$ Prior to 1993 when the U.S. adopted airspace classes, the surface area surrounding an airport that was "controlled airspace" was called a "control zone (CZ)." So I believe the surface area of class E airspace was essentially designed to replace "CZ's." From my 1979 copy of FAR 91 the same reg (91.105 then) states: (paraphrasing for space) except for svfr, no person may operate VFR, within a CZ beneath the ceiling when the ceiling is less than 1000 ft. CZ's were not as large as some current class E surface airspace. But the ceiling intention, I think, was meant to be the same. $\endgroup$
    – user22445
    Feb 22 at 22:33
  • $\begingroup$ @757toga -- yes, in fact I recall you posted a detailed comment to that effect once before. And yet-- considering that control zones had no defined upper limit-- even then, was it really correct to say that "the entire control zone was IMC"? What if you were above any ceiling? Food for thought... $\endgroup$
    – quiet flyer
    Feb 23 at 0:08
  • $\begingroup$ @quietflyer You are absolutely correct. I meant to say that the lateral dimension of the control zone was IMC. Of course if you were flying above the ceiling in VMC you could operate VFR. Good catch. By the way, the upper limit (as I recall) of a Control Zone was 14,500 ft. and the airspace above (up to FL 180) was called the "Continental Control Area" (CCA) $\endgroup$
    – user22445
    Feb 23 at 0:20

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