Setting altimeters with no radio

"Travis Marlatte" wrote:

Regardless, in this case GPS derived altitude was quite good.

Ron Lee

One of the challenges with GPS fixes (both horizontal and vertical) is that
there is a statistical distribution of the error. Most receivers advertise
being within 15' laterally, 90% of the time. It's that other 10% that you
gotta worry about.

Surveyors improve their accuracy by leaving the GPS receiver stationary to
get a statistical sampling that can reveal the true position.

Travis

Correct point Travis but since I fly VFR I use other references to
develop a "blended" solution. Plus my primary GPS receiver has
integrity to catch the really bad errors (rare).

Ron Lee

WE all need to review, perhaps that is the best thing about
these newsgroups.



"Travis Marlatte" wrote in
message
m...
| "Jim Macklin" wrote
in message
| ...
| The word SHALL has a legal meaning...
| (1) On a magnetic course of zero degrees through 179
| degrees, any odd thousand foot MSL altitude +500 feet
(such
| as 3,500, 5,500, or 7,500); or
|
| You got me. I'll confess. I forgot that those were
actually regulations. I
| fly them. I just forgot they were regs.
|
| -------------------------------
| Travis
| Lake N3094P
| PWK
|
|

Mxsmanic wrote:
Since it is possible to fly without voice radio equipment, and given
that (if I understand correctly) pilots are supposed to have their
altimeters set correctly to a reference located not more than 100
miles from their position, how does an aircraft without a radio keep
its altimeter properly set as it travels?

The aircraft gives not a **** if its altimeter is accurate and is
incapable of adjustment if it did.
-----

- gpsman

Travis Marlatte schrieb:

The discussion was about the life-saving necessity of an accurate altitude
instrument.

Sorry to nitpick, but the discussion was about how to set the altimeter
if you can't get the lastest pressure data with the radio. Some guy
proposed to use the GPS altitude as reference, and then some (other?)
guy stated that you better always fly on GPS altitudes, because it's
more accurate anyway. This was the point when I jumped in and said no,
don't do this.

Only then:

MX was claiming that GPS is inaccurate enough to kill you.

Actually, it can. It's accurate within a few meters (depending on how
"enhanced" it is), but only in some 95% or so of the time and in some
90% or so places (the correct numbers don't matter). Which means that if
you happen to be in the wrong place at the wrong time, believing in the
GPS can actually kill you, at least theoretically. Of course I'm rather
looking out of the window when I fly in VMC, so this isn't an issue in
real life for me.

Stefan

Travis Marlatte writes:

Excuse me? The DoD didn't build all of the GPS receivers out there either.

I wasn't talking about the receivers.

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

Recently, Mxsmanic posted:

Travis Marlatte writes:

Excuse me? The DoD didn't build all of the GPS receivers out there
either.

I wasn't talking about the receivers.

You certainly were, given that your claim was that their altitude
reporting was dangerously inaccurate. No other component in the system
reports a particular altitude. Please try to keep up with your side of a
discussion.

Neil

Stefan wrote:

Actually, it can. It's accurate within a few meters (depending on how
"enhanced" it is), but only in some 95% or so of the time and in some
90% or so places (the correct numbers don't matter). Which means that if
you happen to be in the wrong place at the wrong time, believing in the
GPS can actually kill you, at least theoretically.

Stefan

Actually the 95% number often associated with an accuracy is a
confidence. It is not an availability value. Thus under the
identical conditions 95 times out of a hundred you would be at that
accuracy or better. No value of the other 5% is given and may not be
very much worse. At least in this case not enough to be
life-threatening. Of course if VFR use your eyes and look outside.

Ron Lee

No one has mentioned using the manifold pressure guage as an altimeter.

Mxsmanic wrote:
DR writes:


What do you think the WAAS is "augmenting"?


If it were part of GPS, it couldn't augment itself. QED.


You can wriggle but you haven't answered my question. It's not QED. If
you can't think about it let me help you. The WAAS is NOT a positioning
system is it? What does it *actually* augment?

Cheers

Ron Lee wrote:

DR wrote:

On my 12 channel boat GPS I see a
HDOP of ~1m these days.


HDOP is unitless.


Good point. I'm sorry that I was being so loose. But you could descibe
the 1 sigma dilutuion of precision in terms of distance at your position
and time -right? I was actually amazed to see that my Ryatheon GPS put
my boat right in the center of the correct dock -implying 2m accuracy
(or better)!

Cheers MC