Setting altimeters with no radio

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

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

I have to think about it. Position accuracy is given by this generic
equation:

DOP x UERE x 2 = position accuracy (2 sigma or 95%) where UERE is the
combination of the space and user equipment error sources.

Ron Lee

"Mxsmanic" wrote in message
...

No, it is not. It's especially dangerous for RVSM flight, but it's so
inaccurate that it should never be used for anything, except as a last
resort (if the altimeters disintegrate, or whatever).


It was posed as a possible means to adjust a pressure altimeter with no
radio. I'd say that it is better than nothing, in that case. Since you can't
be NORDO in the IFR system, separation is the responsibility of the pilot's
eyes anyway.

-------------------------------
Travis
Lake N3094P
PWK

"Travis Marlatte" wrote in
t:

Since
you can't be NORDO in the IFR system, separation is the responsibility
of the pilot's eyes anyway.

Maybe you should say you cannot be INTENTIONALLY NORDO (squawking 7600).

It would be pretty hard to maintian visual separation in the clag should
the radios go belly up.

Allen

You can't begin an IFR flight as NORDO, but you certainly
can complete the flight that way.



"Travis Marlatte" wrote in
message
t...
| "Mxsmanic" wrote in message
| ...
|
| No, it is not. It's especially dangerous for RVSM
flight, but it's so
| inaccurate that it should never be used for anything,
except as a last
| resort (if the altimeters disintegrate, or whatever).
|
|
| It was posed as a possible means to adjust a pressure
altimeter with no
| radio. I'd say that it is better than nothing, in that
case. Since you can't
| be NORDO in the IFR system, separation is the
responsibility of the pilot's
| eyes anyway.
|
| -------------------------------
| Travis
| Lake N3094P
| PWK
|
|

"Mxsmanic" wrote in message
...


No, it is not. It's especially dangerous for RVSM flight, but it's so
inaccurate that it should never be used for anything,

Your complete misunderstanding of the GPS system is showing. I have two
GPS's in the plane, one panel mount and one portable. It is rare that
either one is ever off by more than 100 feet in altitude. Using GPS for
your altitude for VFR flight would be perfectly fine.

Newps writes:

Your complete misunderstanding of the GPS system is showing. I have two
GPS's in the plane, one panel mount and one portable. It is rare that
either one is ever off by more than 100 feet in altitude. Using GPS for
your altitude for VFR flight would be perfectly fine.

I can see the NTSB report now: "Pilot failed to understand limitations
of GPS navigation." But as long as I'm not flying with you, I don't
care. Do what you want.

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

I recently experimented with flying a GPS approach using the GPS
reported altitude as the "altimeter"... First, I flew the GPS approach
track making notes as to the altimeter reading versus the GPS reported
altitude on two GPS units in the cockpit...

Now, knowing the average local offset between the GPS datum circle and
the local ground altitude as reported by the local barometric pressure
altimeter the official pair of altimeters in the pilots lounge... I
wound up with 79 feet as my averaged offset between the GPS datum plane
and the local altimeter... Notice I am emphasizing the word 'local'
here... Your findings will differ with your area and with what they are
doing down inside that Colorado mountain at any given instant...... A
local WAAS transmitter and a WAAS receiver in my plane would, of
course, narrow that altitude difference... Also note the altitude
delta I found is almost within allowable altimeter error...

Anyway, the second trip around I concentrated on flying the altimeter
and IVSI on the
Garmins instead of the altimeter - jeez, are they twitchy; according to
them I never did establish level flight, they always showed either
climb or descent, albeit usually at a rate of ~10 or 20 fpm... Trying
to fly for real with an altitude instrument this twitchy would be
exhausting.. The descent phase on the various legs of the approach was
interesting but doable...

So, my little experiment shows that one can do a GPS approach - after a
fashion - using the GPS altitude reporting... Knowing in advance what
the local differential between the GPS and the cold hard ground would
be nice...

I intend to next fool around with using the GPS IVSI for flying an ILS
in place of the glide slope... I have done this with the barometric
IVSI and had the radar guys watch me... Two times out of three they
said they could not see any divergence... The one time they did see it
I was definitely off the glide slope as I got sloppy on speed control
and wound up too fast...

Fun stuff to do as opposed to droning around in circles...

denny

Newps wrote:
"Mxsmanic" wrote in message
...


No, it is not. It's especially dangerous for RVSM flight, but it's so
inaccurate that it should never be used for anything,

Your complete misunderstanding of the GPS system is showing. I have two
GPS's in the plane, one panel mount and one portable. It is rare that
either one is ever off by more than 100 feet in altitude. Using GPS for
your altitude for VFR flight would be perfectly fine.