"Andrew Gideon" wrote in message
online.com...
[...]
BTW, I've never seen a definition of "cloud" either. I'm not sure I'd use
the "see through" description. Although that does make sense, I think I'd
use a stricter definition: a region with less than VFR visibility.

That is, if there's a chunk of sky with visibility below 3 miles, I'd call
that a cloud.

While I see the appeal in that definition, I don't believe it's the right
one.

That is, "flight visibility" simply refers to how far a pilot can see from
his position. A chunk of airspace smaller than 3 miles cannot possibly have
"visibility below 3 miles". You need at least 3 miles of airspace in order
to see 3 miles.

Perhaps you are using the "3 miles" as a theoretical gauge, where it merely
represents the average density of a 3 mile chunk of airspace through which a
pilot can see, but no farther. But that doesn't help in determining how far
the pilot can see.

Imagine an area of reduced visibility, isolated in an area of 100 mile
visibility, which if it were completely solid would allow the pilot to see
only 2 miles, but which is only 1/2 mile across. The pilot could easily see
through that area, and easily beyond to the required 3 miles. I would not
consider it reasonable to restrict the pilot from flying through that area
of reduced visibility, given that the pilot can continuously maintain 3
miles of visibility, in spite of being within an area of higher density
reduction of visibility.

Of course, all of the above assumes 3 miles visibility is the true minimum
visibility for VFR flight. The actual minimum is 1 mile, under the right
conditions.

I'm not sure exactly why that definition appeals to me, but it does.
Perhaps because it fits with other limitations on VFR flight.

The limitation for visibility is separate from the limitation for cloud
clearances. Invoking the visibility requirements as a way of defining a
cloud is tempting, but misguided, IMHO.

Pete