Mode C Altitude Q - no Kalisman Correction? (Barometric Pressuredeviation correction?)

Being a student pilot, I'm eating up all kinds of info.
So I go through various instrument info, and then get
to the "Mode C Transponder" that sends altitude info.

Is that alt info built in?

If so, is there no correction for barometric pressure changes?

I don't know that it would be severe, but it seems like the
window could be +/- 100 feet from day to day that the controllers
get from the transponder.

Anyone provide some more info on this issue?

Thanks!

Gary

"GEG" wrote in message
...

Being a student pilot, I'm eating up all kinds of info.
So I go through various instrument info, and then get
to the "Mode C Transponder" that sends altitude info.

Is that alt info built in?

If so, is there no correction for barometric pressure changes?

I don't know that it would be severe, but it seems like the
window could be +/- 100 feet from day to day that the controllers
get from the transponder.

Anyone provide some more info on this issue?

Thanks!


There is no barometric adjustment for altitude encoders, they are set to
29.92. The correction for nonstandard pressure is made at the ATC end.

It's easy to understand why it's done this way. If the adjustment was made
by the pilot he could easily enter the wrong value in his encoder and his
altimeter. He'd then be at the wrong altitude and his encoder would provide
the same wrong altitude to ATC. By having the adjustment made at the ATC
end the radar displays the correct altitude and ATC can advise the pilot of
the error.

"GEG" wrote in message
...

Being a student pilot, I'm eating up all kinds of info.
So I go through various instrument info, and then get
to the "Mode C Transponder" that sends altitude info.

Is that alt info built in?

If so, is there no correction for barometric pressure changes?


By the way, it's Kollsman, not Kalisman.

GEG wrote:

Is that alt info built in?

Yes.

If so, is there no correction for barometric pressure changes?

No.

I don't know that it would be severe, but it seems like the
window could be +/- 100 feet from day to day that the controllers
get from the transponder.

True. The equipment at the controllers' end corrects for barometric pressure
fluctuations, so the info the controller sees is pretty accurate.

George Patterson
There's plenty of room for all of God's creatures. Right next to the
mashed potatoes.

True. The equipment at the controllers' end corrects for barometric
pressure fluctuations, so the info the controller sees is pretty accurate.

George Patterson
There's plenty of room for all of God's creatures. Right next to the
mashed potatoes.

and when the altimeter settings get loaded into the ATC computer
incorrectly.. he sees that everyone is off altitude by the same error
factor..

BT

and when the altimeter settings get loaded into the ATC computer
incorrectly.. he sees that everyone is off altitude by the same error
factor..
BT


hehehe
Good one! Although the separation would at least be correct....

At CLE, they do indeed change it every time the baro setting
changes...it is noted in the system every time it is changed.

--Don



Don Byrer
Instrument Pilot Commercial/CFI Student
Electronics Technician, RADAR/Data/Comm @ CLE
Amateur Radio KJ5KB

"I have slipped the surly bonds of earth; now if I can just land without bending the gear..."

"Don Byrer" wrote in message
...

....snip...

hehehe
Good one! Although the separation would at least be correct....

....snip...

separation from other aircraft would be correct, but not necessarily from
terrain...

Joe Johnson wrote:

separation from other aircraft would be correct, but not necessarily from
terrain...

Neither would be correct for long. As soon as the controller tells one of the
pilots to fly a particular incorrect altitude and the pilot complies, things
will go to hell in a hurry.

George Patterson
There's plenty of room for all of God's creatures. Right next to the
mashed potatoes.

"George Patterson" wrote in message
news:TuT6e.6556$ff4.2610@trndny08...

Neither would be correct for long. As soon as the controller tells one of
the pilots to fly a particular incorrect altitude and the pilot complies,
things will go to hell in a hurry.


Vertical separation between aircraft would be correct as long as the
affected aircraft are on the same altimeter setting.

True. The equipment at the controllers' end corrects for barometric
pressure fluctuations, so the info the controller sees is pretty accurate.

In our neck of the woods (NZ) they only apply a correction below the
transition altitude - no need for any correction for flight levels.

Assume it's the same in the states