ATC Altimeter Settings

"Matt Barrow" wrote in message =
...
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"John R. Copeland" wrote in message
...
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In the Rockies, there are ground stations at widely varying =
elevations.
I've guessed that ATC might not use settings from airports in deep =
valleys
for enroute settings, wherever more representative values are =
available.
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How would a station be more representative if it was/wasn't in a =
valley or
on a hill top?
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In the case of non-standard lapse rates, the lower the airport,
the more the altimeter differs from true height across mountain peaks.

John R. Copeland wrote:

In the case of non-standard lapse rates, the lower the airport,
the more the altimeter differs from true height across mountain peaks.

Lapse rate is temp and has little effect on the altimeter setting.
Because you are already separated from the ground by 2000 feet it is
much more important that everybody have the same setting. No such thing
as an area altimeter setting.

"Newps" wrote in message =
...
=20
John R. Copeland wrote:
=20
In the case of non-standard lapse rates, the lower the airport,
the more the altimeter differs from true height across mountain =
peaks.
=20
Lapse rate is temp and has little effect on the altimeter setting.=20
Because you are already separated from the ground by 2000 feet it is=20
much more important that everybody have the same setting. No such =
thing=20
as an area altimeter setting.


I think you could say lapse rate has *no* effect on altimeter setting.
QNH is whatever it takes to make the altimeter read right on the =
airport.
Lapse rate departure from standard, however, is the major contributor
to any difference between true height and altimeter reading aloft.
Humidity is a minor contributor by comparison.

Lapse rate is lapse rate, whether the station is 2000 feet higher or lower.

"John R. Copeland" wrote in message
...
"Newps" wrote in message
...

John R. Copeland wrote:

In the case of non-standard lapse rates, the lower the airport,
the more the altimeter differs from true height across mountain peaks.

Lapse rate is temp and has little effect on the altimeter setting.
Because you are already separated from the ground by 2000 feet it is
much more important that everybody have the same setting. No such thing
as an area altimeter setting.


I think you could say lapse rate has *no* effect on altimeter setting.
QNH is whatever it takes to make the altimeter read right on the airport.
Lapse rate departure from standard, however, is the major contributor
to any difference between true height and altimeter reading aloft.
Humidity is a minor contributor by comparison.