"Steven P. McNicoll" wrote in message
ink.net...

"Stan Prevost" wrote in message
...

Yes, and I am trying to teach you this basic stuff, but you are very
resistant to instruction.


Well, that explains a lot! Here I thought I was trying to teach you and
it turns out you're teaching me! D'oh! Well, I'm always eager to learn.
Let's press on!


We all can continue to learn a few things, if willing. And I have learned a
few things from you.



You have agreed in previous posts that 91.155(a) defines VFR conditions
and that 91.155(c) defines a restriction on VFR operations under certain
conditions. I'm glad that you understand that. Now let's see if we can
move you to the next level.


I'm aware of only one condition in FAR 91.155(c), a ceiling of less than
1,000 feet. What condition or conditions am I missing?


That it be a surface area.

And you are assigning a meaning to the paragraph which is incorrect. You
seem to be saying that if the reported visibility is three miles are greater
and if there is not a reported ceiling of less than 1000 feet, then VFR
conditions exist. It does not say that at all. It says what it says, which
is that flight under VFR is prohibited in a surface area if there is a
ceiling of less than 1000 ft. And it does not say reported conditions, it
says conditions. It is a rule for pilots ("no person may operate an
aircraft....") and pilots may not operate under VFR in a surface area unless
they comply with both 91.155(a) and 91.155(c). 91.155(c) grants no
exception to 91.155(a), it only defines an additional restriction. Until
you understand and accept this, you will make no progress.

91.155(c) says nothing about visibility. That appears only in 91.155(a)
where it defines visibility requirements in terms of flight visibility. You
can't be selective about what provisions of 91.155(a) you want to apply.



Just to have a clear common reference, I quote the P/CG, which applies to
both pilots and controllers: VFR CONDITIONS- Weather conditions equal to
or better than the minimum for flight under visual flight rules.

91.155(a) defines two things. One is a meteorological limit for VFR
operations, which is flight visibility. The second is an operational
restriction on pilots regarding how closely they may operate to clouds
under VFR. There is no other restriction in that paragraph regarding
clouds, such as ceiling, broken, overcast, scattered, etc.

If sufficient flight visibility exists for the airspace and other
conditions (day/night, altitude), then a pilot may conduct VFR operations
in those conditions as long as s/he is able to maintain the required
cloud
clearance, unless further restricted, such as by 91.155(c). We then say
that VFR conditions exist, in accordance with the P/CG definition. If
the
flight visibility falls below the required minimum value, then VFR
conditions do not exist. If the clouds where the operations are to be
conducted become such that a pilot is unable to maintain the required
cloud clearance, whether vertical or horizontal, then VFR conditions do
not exist because the conditions are such that they will not allow VFR
operations to be conducted in accordance with 91.155(a).

A ceiling higher than 1000 and reported visibility greater than 3 miles
does not assure VFR conditions at an airport. The cloud condition must
be
such that VFR operations can be conducted in accordance with 91.155(a).
It is not uncommon under scud-type conditions for there to be scattered
clouds below the ceiling that will prevent being able to maintain the
required lateral clearance (and flight visibility). Under this
condition,
VFR conditions do not exist.


Interesting. Just to clarify, you're saying that clouds covering 3 to 4
octas of the celestial dome can require flight within a surface area to be
done only by IFR or SVFR? Is that correct? And you say this is not
uncommon? Odd, I've been flying for thirty years and making weather
observations for twelve and it certainly seems uncommon to me.


Just to clarify, what I said is in the text you quoted above, which reads in
part "If the flight
visibility falls below the required minimum value, then VFR conditions do
not exist. If the clouds where the operations are to be conducted become
such that a pilot is unable to maintain the required cloud clearance,
whether vertical or horizontal, then VFR conditions do not exist because the
conditions are such that they will not allow VFR operations to be conducted
in accordance with 91.155(a)." See, you are being resistant to instruction.
And you are suggesting that as a pilot you are willing to violate 91.155(a).


Is there anyone out there still reading this thread that can concur with
Stan's position?

My position is what I stated.




If there is a ceiling and it is less than 1000 ft, then 91.155(c)
prohibits VFR operations below that ceiling in a surface area designated
for an airport. Since flight under VFR cannot be conducted due to a
prohibition based on a meteorological condition, we can say that VFR
conditions do not exist below the ceiling. But if there is a ceiling
greater than 1000 ft and reported visibility is greater than 3 miles,
that
does not mean that VFR conditions do exist below the ceiling.


Then how does a controller ensure that weather conditions at the airport
are VFR prior to issuing a clearance for a visual approach in a surface
area?


I don't know if there is any way, and have never suggested that I do. The
first step for a controller is to learn what the rule actually says, which I
am trying to help you with, and accept its actual meaning, not confusing
that with what may be done in practice. The next step for a controller is
to see if s/he can figure out a way to determine how to correctly comply
with the actual meaning of the rule. If no such way can be determined, then
that controller must decide whether to not issue a visual approach clearance
under conditions which cannot be determined to be in compliance with the
Order or to adopt practices which are not in strict accordance with the
Order. I believe the latter is what is commonly (or universally) done in
practice by ATC, but it ought to be done with proper understanding.



So regarding the requirement for ATC to ensure that VFR conditions exist
at the airport before issuing a clearance for a visual approach, we can
see that 1000/3 in a surface area is necessary but is not sufficient.

I hope this helps you to clarify your understanding.


Not completely. What are the minimum conditions required prior to issuing
a visual approach in a surface area?


That VFR conditions exist.