Setting altimeters with no radio

"Jim Macklin" wrote in message
...
GPS, even a $100 hikers model will solve the problem. But I
just say, look at the ground, you can judge 1,000 feet
pretty well and you only need to apply the hemisphere rule
above 3,000 AGL.


On the other hand, we always tell airport noise complainers that it is very
hard to accurately judge aircraft distances, such as whether the plane is
500 feet or 1000 feet high.

"Jim Macklin" writes:

GPS, even a $100 hikers model will solve the problem. But I
just say, look at the ground, you can judge 1,000 feet
pretty well and you only need to apply the hemisphere rule
above 3,000 AGL.

GPS is far less accurate than an altimeter, and I don't think the
regulations say "if you have no radio, use GPS."

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TxSrv writes:

For VFR, an adjustable altimeter is not required. Therefore, such
a 100 mile rule doesn't exist.

OK. But in that case how do VFR flights maintain specific altitudes?

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Jim Logajan writes:

You can find the answer in FAR 91.121(a)(iii).

Found it, thanks. I'm surprised that just setting it at the airport
would suffice--one could conceivably fly for hundreds of miles VFR,
and the altimeter could change significantly along the way.

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Recently, Mxsmanic posted:

"Jim Macklin" writes:

GPS, even a $100 hikers model will solve the problem. But I
just say, look at the ground, you can judge 1,000 feet
pretty well and you only need to apply the hemisphere rule
above 3,000 AGL.

GPS is far less accurate than an altimeter, and I don't think the
regulations say "if you have no radio, use GPS."

I'm not sure why you think that "GPS is far less accurate than an
altimiter...", as an altimeter only need be accurate to 75' to be legal.
GPS can do much better than that, and are unaffected by barometric
pressure; the result is a potential source of problems that require pilots
to fly by the altimeter, not the GPS. None of this has anything to do
with regulations, of course.

To answer your original question, the prudent pilot will take the
barometric pressure of their destination into consideration during
preflight planning, and adjust the altimeter accordingly. Most of the
time, the pressure won't change all that drastically at the destination in
the time it takes to fly 100 miles, and non-radio VFR pilots aren't likely
to fly in weather where the pressure is changing too rapidly.

Neil

Recently, Mxsmanic posted:

Jim Logajan writes:

You can find the answer in FAR 91.121(a)(iii).

Found it, thanks. I'm surprised that just setting it at the airport
would suffice--one could conceivably fly for hundreds of miles VFR,
and the altimeter could change significantly along the way.

That really isn't as likely as you think, as the flights you're referring
to only takes a couple of hours. If the pressure is changing significantly
faster than that, it's likely to look pretty ugly outside either before
you leave or en-route.

Neil

I think we can judge 1000' from the air better than somebody on the ground
because we spend a lot of time in the pattern at 1000' agl. We gt used to
the perspective and can verify it with our altimeters.

mike

"Super Dave" wrote in message
ink.net...

"Jim Macklin" wrote in message
...
GPS, even a $100 hikers model will solve the problem. But I
just say, look at the ground, you can judge 1,000 feet
pretty well and you only need to apply the hemisphere rule
above 3,000 AGL.


On the other hand, we always tell airport noise complainers that it is
very
hard to accurately judge aircraft distances, such as whether the plane is
500 feet or 1000 feet high.

they give altitude, accurate to within a few feet. just set
the altimeter to read the same. then you know adjusted
pressure. considering the legal requirements, it is
perfectly adequate.

see http://mtp.jpl.nasa.gov/notes/altitude/altitude.html



"Peter Duniho" wrote in
message ...
| "Jim Macklin" wrote
in message
| ...
| GPS, even a $100 hikers model will solve the problem.
|
| No, it won't.
|
|

Looking down you're eye sees details of known sizes, roads,
cars and houses. It is also able to see angles and
relations on the surface. Judging altitude from the air is
fairly easy. I always require my pre-solo students to fly
the traffic pattern [dual] with all the instruments covered.
I have them tell me their altitude and speed and then
uncover the instruments. They are always within 100 feet of
the correct altitude.

On the other hand, looking up, there are no references to
judge height. Is it a full size B52 or a model, is it 2
miles away or 25, the human eye /brain needs reference
points. But a trained observer is taught how to get those
references, such as the size of the airplane, the relation
of their thumb at arms length and the object, etc.



"Super Dave" wrote in message
ink.net...
|
| "Jim Macklin" wrote
in message
| ...
| GPS, even a $100 hikers model will solve the problem.
But I
| just say, look at the ground, you can judge 1,000 feet
| pretty well and you only need to apply the hemisphere
rule
| above 3,000 AGL.
|
|
| On the other hand, we always tell airport noise
complainers that it is very
| hard to accurately judge aircraft distances, such as
whether the plane is
| 500 feet or 1000 feet high.
|
|

right
"mike regish" wrote in message
news |I think we can judge 1000' from the air better than
somebody on the ground
| because we spend a lot of time in the pattern at 1000'
agl. We gt used to
| the perspective and can verify it with our altimeters.
|
| mike
|
| "Super Dave" wrote in message
|
ink.net...
|
| "Jim Macklin"
wrote in message
| ...
| GPS, even a $100 hikers model will solve the problem.
But I
| just say, look at the ground, you can judge 1,000 feet
| pretty well and you only need to apply the hemisphere
rule
| above 3,000 AGL.
|
|
| On the other hand, we always tell airport noise
complainers that it is
| very
| hard to accurately judge aircraft distances, such as
whether the plane is
| 500 feet or 1000 feet high.
|
|
|
|