Setting altimeters with no radio

My IFR GPS, a King KLN90B is connected to the altimeter in my
transponder. It is also adjustable to the barometric setting.

No it isn't coupled to your transponder..............at all. Your encoding
altimeter is inputed to the transponder.

GPS altitude isn't accurate enough.

Karl
"Doug" wrote in message
oups.com...
My regular altimeter broke, and while it was being fixed I flew using
the altimeter in my IFR GPS -- which is coupled to the altimeter in my
transponder--and which BTW has an adjustment for barometer reading. I
am not sure exactly how it works, I think it uses both GPS and the
transponder altimeter reading. It was King KLN90B and a King
transponder, if that matters.

No. It isn't!

Karl
"Doug" wrote in message
oups.com...
My IFR GPS, a King KLN90B is connected to the altimeter in my
transponder. It is also adjustable to the barometric setting.

"Doug" wrote:

My regular altimeter broke, and while it was being fixed I flew using
the altimeter in my IFR GPS -- which is coupled to the altimeter in my
transponder--and which BTW has an adjustment for barometer reading. I
am not sure exactly how it works, I think it uses both GPS and the
transponder altimeter reading. It was King KLN90B and a King
transponder, if that matters.


If your GPS unit has integrity (RAIM) then it can use the transponder
altitude as a pseudo-satellite thus increasing RAIM availability.

Ron (Who apparently knows nothing about GPS" Lee

Recently, Mxsmanic posted:

Neil Gould writes:

I'm not sure why you think that "GPS is far less accurate than an
altimiter..." ...

Because I studied GPS for a long time and was using it before anyone
else knew what it was, and I know how badly it measures altitude. GPS
was designed to accurately measure longitude and latitude; at best, it
gives only a rough estimate of altitude (ships and troops, the
original users of GPS, don't need to know their altitudes).

Ever hear of WAAS?

From the Garmin site: "A WAAS-capable receiver can give you a position
accuracy of better than three meters 95 percent of the time. "

My experience with my 295 bears this out.

Neil

(Ron Lee) wrote:

"Doug" wrote:

My regular altimeter broke, and while it was being fixed I flew using
the altimeter in my IFR GPS -- which is coupled to the altimeter in my
transponder--and which BTW has an adjustment for barometer reading. I
am not sure exactly how it works, I think it uses both GPS and the
transponder altimeter reading. It was King KLN90B and a King
transponder, if that matters.


If your GPS unit has integrity (RAIM) then it can use the transponder
altitude as a pseudo-satellite thus increasing RAIM availability.

Ron (Who apparently knows nothing about GPS" Lee


Correction... Encoding altimeter input is the additional source for
RAIM determination.

Ron Lee

"Peter Duniho" wrote in message ...
: "Jim Macklin" wrote in message
: ...
: 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.
:
: First of all, no they don't give altitude accurate to within a few feet.
: Secondly, they give a completely different kind of altitude measurement than
: the altimeter provides. Even if the GPS were accurate to within feet for
: altitude, setting your altimeter to the GPS displayed altitude would not be
: the same as having the current, local altimeter setting.
:
: Pete
:
:

What about GPS precision approaches...where does the glideslope information come from?


WAAS?

Mxsmanic wrote:
mike regish writes:

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

Nope. GPS is height above the mean surface of the geoid, altimeter is
height above mean sea level. They can be hundreds of feet apart.

You're thinking of height above the ellipsoid, which can be hundreds of
feet different from height above the geoid. But the geoid does
represent the mean sea level height - including in places that are far
from the sea. Internally GPS receivers generally initially calculate
height relative to the ellipsoid model of the earth's shape (using the
WGS-84 model parameters). However, recent models with which I'm
familiar then apply a correction term based on an internal lookup table
to convert the ellipsoid height to the geoid height (equivalent to
height above MSL) at that particular location. See:
http://www.esri.com/news/arcuser/0703/geoid1of3.html
The altitudes that end up being displayed by the GPS after its internal
correction are therefore based on elevation above MSL with some
measurement uncertainty that's dependent on the current satellite
geometry.

How about doing a touch and go at an airport with a known altitude,
while you are retracting flaps, quick twist of the dial to set field
elevation and away you go.

(this was a joke by the way, much as the original question)

Neil Gould wrote:
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

"Ron Lee" wrote

Not sure what he can help on since I understand GPS quite well. I
also fly in mountainous terrain which I doubt that he does.

I think you missed seeing Karl's tongue, planted firmly in his cheek.
--
Jim in NC