Estimating Visibility in Flight
Beverly Wilcox
FAR 61.93.e.3 (formerly 61.93.c.ii) requires CFIs to provide flight
training on "estimating visibility in flight" prior to signing a student
off for solo cross country.
Somewhere, years ago, I saw a paragraph on how estimate flight
visibility in one of the standard FAA books. It was something like,
climb until you can't see the ground, then for every 1000 feet of
altitude you have 1 mile of flight visibility.
I can't find the passage anymore, does anyone remember what it is?
Also, this doesn't seem like such a great idea to me anyway -- anybody
have a better one?
Thanks,
Bev
Eric Wickberg
Beverly, this information is in the "Pilots Handbook of aeronautical
knowledge" (AC 61-23B) pages 190-192, and lists a couple different ways of
determining that, including calculating the "cockpit cutoff angle" for a
particular plane and translating that. Too much info to post, but a
worthwhile read.
Regards,
Eric
Beverly Wilcox
It was right under my nose! Thanks s-o-o-o much. You are a prince and
a scholar (and probably a heck of a flight instructor too). Bev
Q Salt
> Also, this doesn't seem like such a great idea to me anyway -- anybody
> have a better one?
>
> Thanks,
>
> Bev
Probably the best thing to do Bev, is just learn from experience. When
you`re out flying, use a known distance to measure vis and get in the habit
of doing it (You`ll learn this very quickly if you`re in So Cal)
For example, if you`re flying out of a field that`s arond 2,600 feet long,
that`s a half a mile. You can run it in your mind like a ruler to see how
many lengths will bring you to the end of your vis.
Easier yet is to take a known distance between two points. If you`ve got
your chart on your lap, and you know that it`s say ten miles to a certain
town from your present pos, and you can just barely see the town, then the
vis is ten miles. It`s not really al that accurate a system, but it`ll do!
Q
Alexander Perry
Yep, that's what I was told and it works fine; we practiced a bit
in pretty crummy conditions and it really works. However, it
relies on
- a consistent pitch attitude (I use Va with clean,
which is what I fly in poor visibility conditions).
- a consistent seat position (with respect to cockpit coaming).
For the setup I happen to like flying a C172 in, this works out
to be within 10% of the 1000'=1SM rule of thumb.
Put it this way, I originally thought it didn't work right,
because I was trying to get 1000ft=1NM (which was off a lot).
Beverly Wilcox <bmwi...@ucdavis.edu> wrote:
> FAR 61.93.e.3 (formerly 61.93.c.ii) requires CFIs to provide flight
> training on "estimating visibility in flight" prior to signing a student
> off for solo cross country.
>
> Somewhere, years ago, I saw a paragraph on how estimate flight
> visibility in one of the standard FAA books. It was something like,
> climb until you can't see the ground, then for every 1000 feet of
> altitude you have 1 mile of flight visibility.
>
> I can't find the passage anymore, does anyone remember what it is?
>
> Also, this doesn't seem like such a great idea to me anyway -- anybody
> have a better one?
>
> Thanks,
>
> Bev
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John R. Johnson
However, I remember many days in the midwest where there is a solid
stratus deck at about 2000 feet, with thirty mile visibility under it.
The system isn't very workable when there is a relatively low ceiling.
John
Alexander Perry
"John R. Johnson" <jo...@siu.edu> wrote:
> However, I remember many days in the midwest where there is a solid
> stratus deck at about 2000 feet, with thirty mile visibility under it.
> The system isn't very workable when there is a relatively low ceiling.
Yeah, I've seen that (but not here, when flying).
Here, what worries me is a 4000 ft layer of high humidity air,
sitting under an inversion layer. Inside this layer, 5SM in haze.
At the inversion point, isolated scattered (or clear).
Above the layer, clear sky and 40 SM or so.
It isn't like L.A., with brown soup trapped in the valley.
It's a pale white sea in San Diego, and my first thought as I
drop into it is ... will I be able to see obstructions ?
Looking over the nose works fine for that situation.
Someone suggested looking ahead for a feature and counting
seconds until you pass over it. However, I find it difficult
to count for a couple of minutes (accurately) without a stopwatch.
Another trick I came across is to do a standard rate turn and
see how big it is compared to the visible range. A 2 min turn
at 90 knots (Va for a 172) is a mile in diameter. If you can
see a lot further than the other side of the circle, you're fine.
I haven't tried this one though.
Jason Watson
Estimating flight vis is important, don't get me wrong, but if a controller ever asks you
what the vis is, it's always 3 miles. Period.
Jason
patterson,george r
In article <3463D9...@ucdavis.edu>,
Beverly Wilcox <bmwi...@ucdavis.edu> wrote:
>Somewhere, years ago, I saw a paragraph on how estimate flight
>visibility in one of the standard FAA books. It was something like,
>climb until you can't see the ground, then for every 1000 feet of
>altitude you have 1 mile of flight visibility.
>
>Also, this doesn't seem like such a great idea to me anyway -- anybody
>have a better one?
Sounds like something dreamed up either by an armchair warrior or a
fighter pilot with gobs of power. Just thinking back on flights I've
made, I can't remember a single case in which it would have been
practical to do this (plug in the rate of climb of your aircraft and
work out how long it would take for you to determine that you have ten
miles visibility using this method).
In addition, I would bet that there are many weather conditions in which
it is simply untrue. You might get above a haze layer, be unable to see
the ground at 6,000 feet, yet have unlimited visibility. Over light fog,
you might be able to see the ground at nearly any altitude, yet have
little horizontal visibility at ground level.
I've had a LORAN unit in my plane for years. This gives me a fair idea
of the distance to various items (controlled airspace I'm avoiding,
destination airports, etc.). I believe that I've gotten pretty good at
estimating visibilities when I'm within 5,000' of the ground by having
used the LORAN in the past to show me what "five miles away" really
looks like. The people with GPS have a good idea of what 3.27891 miles
away looks like. :-)
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