Setting altimeters with no radio

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.
|
|

Jim Macklin schrieb:
they give altitude, accurate to within a few feet. just set
the altimeter to read the same.

NO, dont' do this. The whole aviation system (airspace, separation...)
is based on pressure altitude, not geometric altitude.

Stefan

Well, kind of. Most, if not all altimeters now, compensate for pressure
variations to show geometric (if that's the right term for it) altitude.

With SA disables in the GPS system, altitude is much more accurate than it
was. How accurate, I don't know. When I compare my altimeter with my GPS's,
they're usually about 100' apart. I'm not sure which is more accurate.

mike

"Stefan" wrote in message
. ..
Jim Macklin schrieb:
they give altitude, accurate to within a few feet. just set the
altimeter to read the same.

NO, dont' do this. The whole aviation system (airspace, separation...) is
based on pressure altitude, not geometric altitude.

Stefan

The question was IF no radio available to get a corrected
altimeter setting... if a GPS is available the GPS altitude
is better than no correction at all.

If I take-off in a airplane with no radio and fly through a
cold front in VFR, the altimeter setting is likely to change
enough to have a 500 foot or greater error with a 100 mile
flight. A GPS can be used to get closer than that.

Probably, most NORDO flights are at or below 3,000 AGL under
VFR. Terrain clearance is more critical to such a flight
based on the altimeter than is the mid-air collision problem
since the "rule" only applies above 3,000 AGL.

Someday, the rules may change, but within today's rules,
using GPS "as the best available" or only source is better
than no source at all.



"mike regish" wrote in message
. ..
| Well, kind of. Most, if not all altimeters now, compensate
for pressure
| variations to show geometric (if that's the right term for
it) altitude.
|
| With SA disables in the GPS system, altitude is much more
accurate than it
| was. How accurate, I don't know. When I compare my
altimeter with my GPS's,
| they're usually about 100' apart. I'm not sure which is
more accurate.
|
| mike
|
| "Stefan" wrote in message
| . ..
| Jim Macklin schrieb:
| they give altitude, accurate to within a few feet.
just set the
| altimeter to read the same.
|
| NO, dont' do this. The whole aviation system (airspace,
separation...) is
| based on pressure altitude, not geometric altitude.
|
| Stefan
|
|

Jim Macklin schrieb:
The question was IF no radio available to get a corrected
altimeter setting... if a GPS is available the GPS altitude
is better than no correction at all.

Agreed.

Probably, most NORDO flights are at or below 3,000 AGL under
VFR. Terrain clearance is more critical to such a flight

In such a flight you usually just look out of the window for terrain
clearance.

Stefan

Agreed also, but if at night, the ground can be hard to see
if there is no moon or ground lights. The question is some
what academic, even aircraft without radios often have a
handheld and altimeter settings can be had from ATIS, etc.

The point about GPS, it is accurate in relation to terrain.
It is not good for IFR separation or ATC boundaries.


"Stefan" wrote in message
...
| Jim Macklin schrieb:
| The question was IF no radio available to get a
corrected
| altimeter setting... if a GPS is available the GPS
altitude
| is better than no correction at all.
|
| Agreed.
|
| Probably, most NORDO flights are at or below 3,000 AGL
under
| VFR. Terrain clearance is more critical to such a
flight
|
| In such a flight you usually just look out of the window
for terrain
| clearance.
|
| Stefan

"Jim Macklin" writes:

The point about GPS, it is accurate in relation to terrain.

It is dangerously inaccurate with respect to terrain.

--
Transpose mxsmanic and gmail to reach me by e-mail.

"Jim Macklin" writes:

If I take-off in a airplane with no radio and fly through a
cold front in VFR, the altimeter setting is likely to change
enough to have a 500 foot or greater error with a 100 mile
flight. A GPS can be used to get closer than that.

Unfortunately, no, it cannot.

Probably, most NORDO flights are at or below 3,000 AGL under
VFR. Terrain clearance is more critical to such a flight
based on the altimeter than is the mid-air collision problem
since the "rule" only applies above 3,000 AGL.

GPS altitudes are especially dangerous to use near the ground, becuase
they are so inaccurate.

Someday, the rules may change, but within today's rules,
using GPS "as the best available" or only source is better
than no source at all.

True, if you are far from the ground and you cannot see the ground.
Don't trust it to keep you clear of terrain at low altitudes.

--
Transpose mxsmanic and gmail to reach me by e-mail.

mike regish schrieb:

When I compare my altimeter with my GPS's,
they're usually about 100' apart. I'm not sure which is more accurate.

The point is not which one is more accurate. The point is that everybody
uses the same frame of reference.

Stefan

My point is that they both are, basically, the same frame of
reference-height above sea level.

mike

"Stefan" wrote in message
...
mike regish schrieb:

When I compare my altimeter with my GPS's, they're usually about 100'
apart. I'm not sure which is more accurate.

The point is not which one is more accurate. The point is that everybody
uses the same frame of reference.

Stefan