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If you're talking about a big puffy cumulus cloud it's pretty obvious. But from where I am right now, looking up I see grey sky from horizon to horizon. But visibility at the surface is good. All nearby metar's are reading 10SM CLR. It's just a tiny bit hazy, but I can clearly see a water tower that is 8 miles from me. But there is no defined cloud layer. It just seems that the haze gets thicker the higher you go. If there was a vfr plane up there at a few thousand feet I'm sure I could see it but I can't see any of the four airliners that FR24 shows are above me.

My question is, when there's no defined cloud layer, what is considered "cloud" and what isn't? If the minima require you to stay 500 feet below clouds, where exactly is that? With metars showing no ceiling how do you know where it is safe to fly and where there might be an ifr flight descending that can't see you?

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    $\begingroup$ I don't know about the FARs, but my instructor told me, "If you can see through it for a distance of 3NM (or visually down 500 ft, or visually up 1000ft), then its not a cloud; its just some moisture." $\endgroup$
    – abelenky
    Feb 23 '17 at 22:13
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    $\begingroup$ My CFI pretty much mirrored what @abelenky 's CFI did, "if you can see through it, don't worry about it". $\endgroup$
    – Ron Beyer
    Feb 23 '17 at 22:43
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    $\begingroup$ "That's not a cloud - that's a region of temporarily reduced visibility." $\endgroup$
    – pericynthion
    Feb 24 '17 at 0:58
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My question is, when there's no defined cloud layer, what is considered "cloud" and what isn't? If the minima require you to stay 500 feet below clouds, where exactly is that? With metars showing no ceiling how do you know where it is safe to fly and where there might be an ifr flight descending that can't see you?

The FAA defines clouds in AC-006B

A cloud is a visible aggregate of minute water droplets and/or ice particles in the atmosphere above the Earth’s surface. Fog differs from cloud only in that the base of fog is at the Earth’s surface while clouds are above the surface. Clouds are like signposts in the sky that provide information on air motion, stability, and moisture. Clouds help pilots visualize weather conditions and potential weather hazards.

However legally and practically speaking you can fly as high as you like if there are no clouds provided you can maintain situational awareness and proper cloud clearances from any adjacent clouds (including those under you). There are a few practical limits to this. First off Class A airspace starts at FL180 so you cant fly above 18,000 Ft. without being on an IFR flight plan since you cant fly VFR into class A. Further more, since you seem to be asking about small aircraft, you will more than likely be limited by your airframes maximum altitude before hitting the Class A limit. You will also need O2 onboard to fly above 12,500 ft.

The risk of a descending aircraft above you is always a concern be it VFR or IFR flying as they generally cant see below them and you cant always see above you when flying. In many cases the IFR flight will have some help from ATC who will see you on radar even if you are flying VFR and squawking 1200 on your transponder.

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  • $\begingroup$ In the US, only student pilots need to maintain sight of the ground. Once you have your PPL, you can fly over cloud cover—I do it all the time. It even has a name—VFR Over-the-Top. I don’t believe that there is a requirement to maintain visibility with the horizon for either student or PPL. $\endgroup$
    – JScarry
    Feb 24 '17 at 0:01
  • $\begingroup$ You are correct that you can fly Over-the-Top, the horizon issue is somewhat addressed in this question Something made me think you also needed to see the ground but im looking into it now. You may in-fact be correct. However not being able to see the ground or the horizon may be considered IMC. $\endgroup$
    – Dave
    Feb 24 '17 at 0:24
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    $\begingroup$ By "VFR flight conditions" you mean VMC? $\endgroup$
    – DJClayworth
    Feb 24 '17 at 1:47
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    $\begingroup$ This is one of my pet peeves: When talking about the conditions (moonless night, etc), it should be important to call them either VMC or IMC. When talking about rules, it's VFR or IFR. You must be in VMC to operate under VFR rules. This should not be referred to as "VFR Conditions", because you can also operate under a different set of rules (IFR) in those same conditions (VMC). Unfortunately, even the FAR and AIM both use the term, "VFR Conditions" -- which in my opinion is a term that needs to be nixed from all literature. Too much confusion has been had by intermingling terms. $\endgroup$
    – Jimmy
    Feb 24 '17 at 2:19
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    $\begingroup$ Thanks, @jscarry, and good reference! My comment was only on the phraseology that you used: "IFR time". My statement was that "Instrument time" is the more correct term. In the US, pilot's don't log "IFR Time", because that phrase implies any flight where they are on an IFR flight plan and under ATC control. The entire flight would be considered "IFR Time", but not necessarily "instrument time". US Pilots only log "Instrument Time" during meteorological conditions met in 61.51, no matter if they are on an IFR flight or VFR flight. (and the caveat that I believe Euro pilots do log "IFR Time") $\endgroup$
    – Jimmy
    Feb 24 '17 at 23:59

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