When entering an ATC region, we often get an altimeter setting, usually
at some fix. So for example, when entering the Chicago center ATC
region, they say something like, "Midway altimeter is xx.xx." I have
some questions.

1. So, do they pick some fix for the region and give everyone (those
below FL 180) the altimeter of that fix? Do they break up into
sub-regions and give everyone in that sub-region that same fix altimeter
setting?

2. At what point after departing an airport do you change altimeter
setting to the one supplied by ATC? Similarly, on approaching an
airport to land, at what point do you switch over to the altimeter
setting of the airport (from that given by ATC).

The reason I ask is that sometimes, the altimeter settings can be quite
different. Especially if there is VFR traffic around an airport, it
seems that there is some risk if everyone entering the pattern (or
approaching the pattern) does not share the same altimeter setting.

Just curious.

-Sami
N2057M, Piper Turbo Arrow III

O. Sami Saydjari > wrote:
>When entering an ATC region, we often get an altimeter setting, usually
>at some fix. So for example, when entering the Chicago center ATC
>region, they say something like, "Midway altimeter is xx.xx." I have
>some questions.
>
>1. So, do they pick some fix for the region and give everyone (those
>below FL 180) the altimeter of that fix? Do they break up into
>sub-regions and give everyone in that sub-region that same fix altimeter
>setting?

You should get the altimeter setting for the airport nearest your
location which has weather reporting.

> 2. At what point after departing an airport do you change altimeter
> setting to the one supplied by ATC?

I update my altimeter setting whenever ATC gives me a new one.

> Similarly, on approaching an airport to land, at what point do you
> switch over to the altimeter setting of the airport (from that given
> by ATC).

If ATC has given me a setting for my destation, I'll just use that.
If not, then I'll set my altimeter whenever I get the ATIS/AWOS.

> The reason I ask is that sometimes, the altimeter settings can be quite
> different.

What do you consider "quite different"? Unless there's some severe
weather going on, it's unusual to have to change the setting more than
a couple of 1/100's at a time.

> Especially if there is VFR traffic around an airport, it
> seems that there is some risk if everyone entering the pattern (or
> approaching the pattern) does not share the same altimeter setting.

Risk of what? If somebody's 50 feet high or low in the pattern, it
doesn't make much difference. As long as it's VFR, see and avoid is
the rule of the day. The real reason for having sensitive altimeters
is for instrument work.

Roy Smith wrote:

> O. Sami Saydjari > wrote:
>
>>When entering an ATC region, we often get an altimeter setting, usually
>>at some fix. So for example, when entering the Chicago center ATC
>>region, they say something like, "Midway altimeter is xx.xx." I have
>>some questions.
>>
>>1. So, do they pick some fix for the region and give everyone (those
>>below FL 180) the altimeter of that fix? Do they break up into
>>sub-regions and give everyone in that sub-region that same fix altimeter
>>setting?
>
>
> You should get the altimeter setting for the airport nearest your
> location which has weather reporting.

So, if ATC gives you a setting on initial contact out of the airport you
just took off from, you use the airport's setting, not ATC's? When do
you cut over to ATC's? Or do you just listen to every AWOS/ASOS enroute
and change to the closest one?

>
>
>>2. At what point after departing an airport do you change altimeter
>>setting to the one supplied by ATC?
>
>
> I update my altimeter setting whenever ATC gives me a new one.

See above. What I am asking is when to change over?
>
>
>>Similarly, on approaching an airport to land, at what point do you
>>switch over to the altimeter setting of the airport (from that given
>>by ATC).
>
>
> If ATC has given me a setting for my destation, I'll just use that.
> If not, then I'll set my altimeter whenever I get the ATIS/AWOS.

So, ATC expects you to change your altimeter whenever you first hear the
ATIS at your destination? That could be 50 miles out. Seems a little odd.

>
>
>>The reason I ask is that sometimes, the altimeter settings can be quite
>>different.
>
>
> What do you consider "quite different"? Unless there's some severe
> weather going on, it's unusual to have to change the setting more than
> a couple of 1/100's at a time.

I have seen differences of 0.5 inches....that is alot!

>
>
>>Especially if there is VFR traffic around an airport, it
>>seems that there is some risk if everyone entering the pattern (or
>>approaching the pattern) does not share the same altimeter setting.
>
>
> Risk of what? If somebody's 50 feet high or low in the pattern, it
> doesn't make much difference. As long as it's VFR, see and avoid is
> the rule of the day. The real reason for having sensitive altimeters
> is for instrument work.

Well, good point, except that if you are descending through a cloud deck
into VFR conditions. Also, if you change your altimeter 50 miles out
and I change mine 5 miles out, it seems like their is some distance from
the airport where we are using different settings, and that seems like a
bad thing to me.

O. Sami Saydjari > wrote:
>> You should get the altimeter setting for the airport nearest your
>> location which has weather reporting.
>
>So, if ATC gives you a setting on initial contact out of the airport you
>just took off from, you use the airport's setting, not ATC's?

I think I may have confused you with some sloppy wording. What I
meant was, "The altimeter setting ATC gives you will mostly likely be
for the airport nearest your current location".

The bottom line is anytime ATC gives me an altimeter setting, I reset
my altimeter to whatever the controller gives me.

> Or do you just listen to every AWOS/ASOS enroute
> and change to the closest one?

Well, I do that too. Maybe not *every* one, but on a long flight, I
will certainly tune in the occassional ATIS as I go by airports. It's
also a good way to stay aware of weather trends; if the altimeter
settings keep going down, you know you're flying into worsening weather.

>> What do you consider "quite different"? Unless there's some severe
>> weather going on, it's unusual to have to change the setting more than
>> a couple of 1/100's at a time.
>
>I have seen differences of 0.5 inches....that is alot!

0.5 inches is a HUGE altimter setting change. Are you sure about
that?

On 1 Apr 2005 13:56:42 -0500, Roy Smith wrote:

> 0.5 inches is a HUGE altimter setting change. Are you sure about
> that?

I have to agree with Roy here.

I just finished coming back from Ohio to Mississippi, and I experienced a
very large altimeter setting adjustments in my journey southbound north of
Bowling Green KY, but I sure did not experience .50 inches adjustments en
route. I did end up .25 inch less over the whole trip though.

If I remember correctly on one ATC hand off, I went from 29.96 to 29.88
which lowered my altitude by 80 feet. This really alarmed me as I sure
don't like deviating more then 20 feet from assigned altitude. Needless to
say, I made a quick climb to my assigned altitude!

There was a rather steep pressure gradient even in my trip I just did this
week, but as Roy says, .5 inch altimeter change in a flight range distance
in planes I fly is probably indicative of weather I wouldn't / shouldn't be
flying in anyway.

Allen

Well, I thought it was 0.5 inches, but I am not absolutley certain...it
was a while back. But, I do not think this changes my point
substantially. Even a 0.25 inch change is substantial, and if there is
not a standard of when one changes settings, it seems like a risk,
albeit small.

My experience is that ATC does not give me settings of nearby airports.
For example, I recall entering Chicgo Center airspace from the south.
I was just north of Lafayette, Indiana. The controller gave me the
altimeter setting for Chicago Midway. That is a long way away.
Lafayette airport was at least 0.1 inches different. I used ATC's
setting, because I figure they must have some standard reference point
in a region, or sub-region, so that all the planes are at least on the
same relative setting.

-Sami
N2057M, Piper Turbo Arrow III

A Lieberman wrote:

> On 1 Apr 2005 13:56:42 -0500, Roy Smith wrote:
>
>
>>0.5 inches is a HUGE altimter setting change. Are you sure about
>>that?
>
>
> I have to agree with Roy here.
>
> I just finished coming back from Ohio to Mississippi, and I experienced a
> very large altimeter setting adjustments in my journey southbound north of
> Bowling Green KY, but I sure did not experience .50 inches adjustments en
> route. I did end up .25 inch less over the whole trip though.
>
> If I remember correctly on one ATC hand off, I went from 29.96 to 29.88
> which lowered my altitude by 80 feet. This really alarmed me as I sure
> don't like deviating more then 20 feet from assigned altitude. Needless to
> say, I made a quick climb to my assigned altitude!
>
> There was a rather steep pressure gradient even in my trip I just did this
> week, but as Roy says, .5 inch altimeter change in a flight range distance
> in planes I fly is probably indicative of weather I wouldn't / shouldn't be
> flying in anyway.
>
> Allen

On Fri, 01 Apr 2005 14:19:56 -0600, O. Sami Saydjari wrote:

Sami

> Well, I thought it was 0.5 inches, but I am not absolutley certain...it
> was a while back. But, I do not think this changes my point
> substantially. Even a 0.25 inch change is substantial, and if there is
> not a standard of when one changes settings, it seems like a risk,
> albeit small.

The .25 inch change was over 684 NM. Unless you are crossing a cold front
or a rather intense low pressure, you are not too likely to experience a
significant pressure change to the point that you describe.

> My experience is that ATC does not give me settings of nearby airports.
> For example, I recall entering Chicgo Center airspace from the south.
> I was just north of Lafayette, Indiana. The controller gave me the
> altimeter setting for Chicago Midway. That is a long way away.
> Lafayette airport was at least 0.1 inches different.

What day were you flying? If you go to
http://www.hpc.ncep.noaa.gov/dailywxmap/frame.html, you can retrieve
historical weather maps to verify what you say. Was it windy that day?
Was there a low pressure passing through. If so, then yes, it is possible
to experience a .10 inch change over a short range.

> I used ATC's
> setting, because I figure they must have some standard reference point
> in a region, or sub-region, so that all the planes are at least on the
> same relative setting.

I always use ATC's settings. I figure their scope reads my transponder,
and my transponder readout is dependent on what I put in for my altimeter
setting. I sure don't want an altitude deviation based on something
different then what ATC tells me.

Like Roy said, if you are arriving at an airport VFR, the altimeter is not
quite as important as when you are arriving at an airport under instrument
conditions.

It's see and avoid for VFR, and if your altimeter is only .01 off, that
only puts you approximately 10 feet off pattern altitude. .10 would put
you 100 feet off pattern altitude, and again, see and avoid would be the
ruling factor.

It becomes more critical on an instrument approach, as you want to be as
close as you can for an accurate altimeter setting for missed approaches
purposes at MDA or DH.

Allen

"A Lieberman" > wrote in message
...
> On Fri, 01 Apr 2005 14:19:56 -0600, O. Sami Saydjari wrote:
>
> Sami
>
> > Well, I thought it was 0.5 inches, but I am not absolutley certain...it
> > was a while back. But, I do not think this changes my point
> > substantially. Even a 0.25 inch change is substantial, and if there is
> > not a standard of when one changes settings, it seems like a risk,
> > albeit small.
>
> The .25 inch change was over 684 NM. Unless you are crossing a cold front
> or a rather intense low pressure, you are not too likely to experience a
> significant pressure change to the point that you describe.

The only time I had seen a significant change in altimeter setting was when
crossing over from the central valley in California (Bakersfield sector) to
the LA basin (Socal). I remember my altitude was off by 100-150ft which
really bothered me and I could do nothing about it since I switched to the
altimeter setting provided when given to me. One of them was certainly off
for sure. Also, the radio comm was weak in the transition area. The Socal
controller was not too happy.

>
> I always use ATC's settings. I figure their scope reads my transponder,
> and my transponder readout is dependent on what I put in for my altimeter
> setting.

IIRC the Mode C is pressure altitude, usually from a separate transducer.

AIM 7-2-3 says your altimeter can be in error by 74 feet without a trip to
the shop, so at least that much slop is built into the system. The ATC
separates IFR from IFR by miles, not feet (OK, feet vertically, but opposite
direction traffic is separated by at least 1000 feet vertically).

If my preflight weather analysis showed a pressure difference of .5 inches
from one area to another but within my range, I would seriously consider
going somewhere else.

One-tenth of an inch is 100 feet...I would not get ulcers over it.

Bob Gardner


"O. Sami Saydjari" > wrote in message
...
> Well, I thought it was 0.5 inches, but I am not absolutley certain...it
> was a while back. But, I do not think this changes my point
> substantially. Even a 0.25 inch change is substantial, and if there is
> not a standard of when one changes settings, it seems like a risk, albeit
> small.
>
> My experience is that ATC does not give me settings of nearby airports.
> For example, I recall entering Chicgo Center airspace from the south. I
> was just north of Lafayette, Indiana. The controller gave me the
> altimeter setting for Chicago Midway. That is a long way away. Lafayette
> airport was at least 0.1 inches different. I used ATC's setting, because
> I figure they must have some standard reference point in a region, or
> sub-region, so that all the planes are at least on the same relative
> setting.
>
> -Sami
> N2057M, Piper Turbo Arrow III
>
> A Lieberman wrote:
>
>> On 1 Apr 2005 13:56:42 -0500, Roy Smith wrote:
>>
>>
>>>0.5 inches is a HUGE altimter setting change. Are you sure about
>>>that?
>>
>>
>> I have to agree with Roy here. I just finished coming back from Ohio to
>> Mississippi, and I experienced a
>> very large altimeter setting adjustments in my journey southbound north
>> of
>> Bowling Green KY, but I sure did not experience .50 inches adjustments en
>> route. I did end up .25 inch less over the whole trip though.
>>
>> If I remember correctly on one ATC hand off, I went from 29.96 to 29.88
>> which lowered my altitude by 80 feet. This really alarmed me as I sure
>> don't like deviating more then 20 feet from assigned altitude. Needless
>> to
>> say, I made a quick climb to my assigned altitude!
>>
>> There was a rather steep pressure gradient even in my trip I just did
>> this
>> week, but as Roy says, .5 inch altimeter change in a flight range
>> distance
>> in planes I fly is probably indicative of weather I wouldn't / shouldn't
>> be
>> flying in anyway.
>>
>> Allen

"Sriram Narayan" > wrote:
> The only time I had seen a significant change in altimeter setting was when
> crossing over from the central valley in California (Bakersfield sector) to
> the LA basin (Socal). I remember my altitude was off by 100-150ft which
> really bothered me and I could do nothing about it since I switched to the
> altimeter setting provided when given to me. One of them was certainly off
> for sure.

Are you saying that the mode-c altitude your transponder was reporting
differed by 100-150 ft from your indicated altitude? If that's the case,
your indicated altitude is considered the correct one.

Mitty wrote:
>
>>
>> I always use ATC's settings. I figure their scope reads my transponder,
>> and my transponder readout is dependent on what I put in for my altimeter
>> setting.
>
>
> IIRC the Mode C is pressure altitude, usually from a separate transducer.

Yes, everybody's mode C reports a 29.92 altitude that is corrected by ATC.

According to "The Weather Book," by USA Today weather editor Jack Williams,
a one-half-pound pressure difference between places 500 miles apart will
accelerate still air to 80 mph in three hours. Increase the distance to 1000
miles and the windspeed will be 40 mph after three hours. Don't know about
you, but 80 mph surface winds are beyond my meager skills. I think your .5
inch figure is overstated.

Bob Gardner

"O. Sami Saydjari" > wrote in message
...
> Well, I thought it was 0.5 inches, but I am not absolutley certain...it
> was a while back. But, I do not think this changes my point
> substantially. Even a 0.25 inch change is substantial, and if there is
> not a standard of when one changes settings, it seems like a risk, albeit
> small.
>
> My experience is that ATC does not give me settings of nearby airports.
> For example, I recall entering Chicgo Center airspace from the south. I
> was just north of Lafayette, Indiana. The controller gave me the
> altimeter setting for Chicago Midway. That is a long way away. Lafayette
> airport was at least 0.1 inches different. I used ATC's setting, because
> I figure they must have some standard reference point in a region, or
> sub-region, so that all the planes are at least on the same relative
> setting.
>
> -Sami
> N2057M, Piper Turbo Arrow III
>
> A Lieberman wrote:
>
>> On 1 Apr 2005 13:56:42 -0500, Roy Smith wrote:
>>
>>
>>>0.5 inches is a HUGE altimter setting change. Are you sure about
>>>that?
>>
>>
>> I have to agree with Roy here. I just finished coming back from Ohio to
>> Mississippi, and I experienced a
>> very large altimeter setting adjustments in my journey southbound north
>> of
>> Bowling Green KY, but I sure did not experience .50 inches adjustments en
>> route. I did end up .25 inch less over the whole trip though.
>>
>> If I remember correctly on one ATC hand off, I went from 29.96 to 29.88
>> which lowered my altitude by 80 feet. This really alarmed me as I sure
>> don't like deviating more then 20 feet from assigned altitude. Needless
>> to
>> say, I made a quick climb to my assigned altitude!
>>
>> There was a rather steep pressure gradient even in my trip I just did
>> this
>> week, but as Roy says, .5 inch altimeter change in a flight range
>> distance
>> in planes I fly is probably indicative of weather I wouldn't / shouldn't
>> be
>> flying in anyway.
>>
>> Allen

OK, I am convinced that 0.5 inches was overstated.

So are we are concluding that it is best to switch to ATC altimeter
setting as soon as they give them to you, and that differences from
local airport settings, except when you are on approach to your
destination (where you use that airport's setting).

Still, I am curious to hear from a controller, how they pick their
altimeter settings for their region of control. Is it always the same
airport? Is the fix somewhere in the center of their region.

Just curious.

-Sami


Bob Gardner wrote:

> According to "The Weather Book," by USA Today weather editor Jack Williams,
> a one-half-pound pressure difference between places 500 miles apart will
> accelerate still air to 80 mph in three hours. Increase the distance to 1000
> miles and the windspeed will be 40 mph after three hours. Don't know about
> you, but 80 mph surface winds are beyond my meager skills. I think your .5
> inch figure is overstated.
>
> Bob Gardner
>
> "O. Sami Saydjari" > wrote in message
> ...
>
>>Well, I thought it was 0.5 inches, but I am not absolutley certain...it
>>was a while back. But, I do not think this changes my point
>>substantially. Even a 0.25 inch change is substantial, and if there is
>>not a standard of when one changes settings, it seems like a risk, albeit
>>small.
>>
>>My experience is that ATC does not give me settings of nearby airports.
>>For example, I recall entering Chicgo Center airspace from the south. I
>>was just north of Lafayette, Indiana. The controller gave me the
>>altimeter setting for Chicago Midway. That is a long way away. Lafayette
>>airport was at least 0.1 inches different. I used ATC's setting, because
>>I figure they must have some standard reference point in a region, or
>>sub-region, so that all the planes are at least on the same relative
>>setting.
>>
>>-Sami
>>N2057M, Piper Turbo Arrow III
>>
>>A Lieberman wrote:
>>
>>
>>>On 1 Apr 2005 13:56:42 -0500, Roy Smith wrote:
>>>
>>>
>>>
>>>>0.5 inches is a HUGE altimter setting change. Are you sure about
>>>>that?
>>>
>>>
>>>I have to agree with Roy here. I just finished coming back from Ohio to
>>>Mississippi, and I experienced a
>>>very large altimeter setting adjustments in my journey southbound north
>>>of
>>>Bowling Green KY, but I sure did not experience .50 inches adjustments en
>>>route. I did end up .25 inch less over the whole trip though.
>>>
>>>If I remember correctly on one ATC hand off, I went from 29.96 to 29.88
>>>which lowered my altitude by 80 feet. This really alarmed me as I sure
>>>don't like deviating more then 20 feet from assigned altitude. Needless
>>>to
>>>say, I made a quick climb to my assigned altitude!
>>>
>>>There was a rather steep pressure gradient even in my trip I just did
>>>this
>>>week, but as Roy says, .5 inch altimeter change in a flight range
>>>distance
>>>in planes I fly is probably indicative of weather I wouldn't / shouldn't
>>>be
>>>flying in anyway.
>>>
>>>Allen
>
>
>

In article >, Bob Gardner wrote:
> According to "The Weather Book," by USA Today weather editor Jack Williams,
> a one-half-pound pressure difference between places 500 miles apart will
> accelerate still air to 80 mph in three hours. Increase the distance to 1000
> miles and the windspeed will be 40 mph after three hours. Don't know about
> you, but 80 mph surface winds are beyond my meager skills. I think your .5
> inch figure is overstated.

I had a 0.05 difference about 30 miles apart last weekend and thought that
was unusually high.

Morris (what's an order of magnitude among friends?)

"O. Sami Saydjari" > wrote:
> So are we are concluding that it is best to switch to ATC altimeter
> setting as soon as they give them to you

That's what I'm concluding. You?

> and that differences from local airport settings, except when you are on
> approach to your destination (where you use that airport's setting).

I'll always favor an altimeter setting ATC gives me over anything I hear on
the ATIS. The ATIS could be up to an hour old; the controller is looking
at the most current reading right now.

"Bob Gardner" > writes:

> According to "The Weather Book," by USA Today weather editor Jack Williams,
> a one-half-pound pressure difference between places 500 miles apart will
> accelerate still air to 80 mph in three hours. [...]

Does that refer to surface or upper winds?

> [...] I think your .5 inch figure is overstated.

Well, today it's not hard to find two places on the continent with a
0.50 difference in altimeter settings: any place under the big storm
in the north east, and another place far enough, like KORD. That's
only a couple hours' flight in our bugsmashers.


- FChE

"O. Sami Saydjari" > wrote in message
...
> When entering an ATC region, we often get an altimeter setting, usually
> at some fix. So for example, when entering the Chicago center ATC
> region, they say something like, "Midway altimeter is xx.xx." I have
> some questions.
>
> 1. So, do they pick some fix for the region and give everyone (those
> below FL 180) the altimeter of that fix? Do they break up into
> sub-regions and give everyone in that sub-region that same fix altimeter
> setting?
>

Center ATC is divided into Sectors. Each Sector has a series of altimeters
that they monitor. My Center Airspace has three low altitude sectors and 4
high/ultra high sectors that I work on a daily basis. The three low sectors
lie north of Atlanta, between Atlanta GA (ATL), Chattanooga TN (CHA),
Nashville TN (BNA),Knoxville TN (TYS) Asheville NC (AVL) and back to
Atlanta. Each of these low sectors has a set series of altimeter stations
that by facility SOP (standard operating procedure) the sector must monitor.
These stations have been determined by FAA management to be germain to the
safe operation of the sector.

Two of the sectors stack on top of each other, covering North Georgia from
the ground to FL230. These two sectors must monitor (by SOP) the ATL, CHA
and TYS altimeter settings. The other sector lies to the north in
Tennessee. This sector must monitor CHA, CSV (Crossville TN) and TYS
altimeter settings. When the three sectors are combined (as they often
are), then the combined sector must monitor ATL, CHA, CSV and TYS.

The way we monitor the altimeters is that we have them displayed in an
electronic box on the scope. As the weather updates at whatever station we
are monitoring, the altimeters update automatically. If one or more of the
local altimeters that belong to a sector dips below 29.92, then we are no
longer able to use FL180 for IFR separation. In ATC parlance, we say
"Eighteen is broken."

We are required to issue a local altimeter at least once to you as you
transit the sector. I try to use a little common sense on which one I
issue, but in the enroute environment, you are not always going to be flying
directly between or along altimeter stations that I am monitoring. An
example would be a flight from Chattanooga TN to Charelston SC. You have
departed CHA. You are exactly between TYS and ATL. When you check in with
ARTCC, which altimeter do I issue? CHA (which you just left) or one of the
other two which are not on your route? Many of us avoid these awkward
situations by monitoring additional stations. For example, if you depart
TYS heading up towards Cinncinnatti or points north, I will issue you the
London KY altimeter (LOZ) because I think it is stupid to issue you the TYS
altimeter when TYS is 30 miles behind you and LOZ is coming up. So I
monitor LOZ as well in my electronic list, just because...

Chip, ZTL

"Frank Ch. Eigler" > wrote in message
...
>
> "Bob Gardner" > writes:
>
>> According to "The Weather Book," by USA Today weather editor Jack
>> Williams,
>> a one-half-pound pressure difference between places 500 miles apart will
>> accelerate still air to 80 mph in three hours. [...]
>
> Does that refer to surface or upper winds?
>
>> [...] I think your .5 inch figure is overstated.
>
> Well, today it's not hard to find two places on the continent with a
> 0.50 difference in altimeter settings: any place under the big storm
> in the north east, and another place far enough, like KORD. That's
> only a couple hours' flight in our bugsmashers.
>
>

Yes, Detroit to JFK would be just about .5 this evening.

That translates to 500 feet down-error, even if you ignore the "fly toward
the low, look out below" mantra and never adjust the altimeter. Allowing
200 feet altitude-maintenance error, you will still have 300 feet buffer
from the adjacent flight level.

Unless, of course, someone is flying in the opposite direction ALSO ignoring
the mantra, in which case his error will be UP, while yours is DOWN, and
interesting things may result.

So know your weather situation before takeoff, and get QNH updates
frequently along the route in such extreme situations.

"Chip Jones" > wrote in message =
link.net...
>=20
> "O. Sami Saydjari" > wrote in message
> ...
>> When entering an ATC region, we often get an altimeter setting, =
usually
>> at some fix. So for example, when entering the Chicago center ATC
>> region, they say something like, "Midway altimeter is xx.xx." I have
>> some questions.
>>
>> 1. So, do they pick some fix for the region and give everyone (those
>> below FL 180) the altimeter of that fix? Do they break up into
>> sub-regions and give everyone in that sub-region that same fix =
altimeter
>> setting?
>>
>=20
> Center ATC is divided into Sectors. Each Sector has a series of =
altimeters
> that they monitor. My Center Airspace has three low altitude sectors =
and 4
> high/ultra high sectors that I work on a daily basis. The three low =
sectors
> lie north of Atlanta, between Atlanta GA (ATL), Chattanooga TN (CHA),
> Nashville TN (BNA),Knoxville TN (TYS) Asheville NC (AVL) and back to
> Atlanta. Each of these low sectors has a set series of altimeter =
stations
> that by facility SOP (standard operating procedure) the sector must =
monitor.
> These stations have been determined by FAA management to be germain to =
the
> safe operation of the sector.
>=20
> Two of the sectors stack on top of each other, covering North Georgia =
from
> the ground to FL230. These two sectors must monitor (by SOP) the ATL, =
CHA
> and TYS altimeter settings. The other sector lies to the north in
> Tennessee. This sector must monitor CHA, CSV (Crossville TN) and TYS
> altimeter settings. When the three sectors are combined (as they =
often
> are), then the combined sector must monitor ATL, CHA, CSV and TYS.
>=20
> The way we monitor the altimeters is that we have them displayed in an
> electronic box on the scope. As the weather updates at whatever =
station we
> are monitoring, the altimeters update automatically. If one or more =
of the
> local altimeters that belong to a sector dips below 29.92, then we are =
no
> longer able to use FL180 for IFR separation. In ATC parlance, we say
> "Eighteen is broken."
>=20
> We are required to issue a local altimeter at least once to you as you
> transit the sector. I try to use a little common sense on which one I
> issue, but in the enroute environment, you are not always going to be =
flying
> directly between or along altimeter stations that I am monitoring. An
> example would be a flight from Chattanooga TN to Charelston SC. You =
have
> departed CHA. You are exactly between TYS and ATL. When you check in =
with
> ARTCC, which altimeter do I issue? CHA (which you just left) or one =
of the
> other two which are not on your route? Many of us avoid these awkward
> situations by monitoring additional stations. For example, if you =
depart
> TYS heading up towards Cinncinnatti or points north, I will issue you =
the
> London KY altimeter (LOZ) because I think it is stupid to issue you =
the TYS
> altimeter when TYS is 30 miles behind you and LOZ is coming up. So I
> monitor LOZ as well in my electronic list, just because...
>=20
> Chip, ZTL
>=20
>
Chip, you didn't mention enroute altimeter settings being different from =
surface ones.
I've seen that condition in the Rocky Mountains, but I can't =
specifically recall
if I've ever seen it in the central and eastern U.S.
In the west, lapse rates can be such that an altimeter setting for an =
airport
can be noticeably different from the enroute value many thousands of =
feet higher.

The controller may have good reason to issue area altimeter settings =
which are
different from those reported at nearby airports.

John R. Copeland wrote:

>>
>
> Chip, you didn't mention enroute altimeter settings being different from surface ones.
> I've seen that condition in the Rocky Mountains, but I can't specifically recall
> if I've ever seen it in the central and eastern U.S.

Controllers issue altimeter settings from ground stations. Where else
would they come from?

In article >,
Newps > wrote:

> John R. Copeland wrote:
>
> >>
> >
> > Chip, you didn't mention enroute altimeter settings being different from
> > surface ones.
> > I've seen that condition in the Rocky Mountains, but I can't specifically
> > recall
> > if I've ever seen it in the central and eastern U.S.
>
> Controllers issue altimeter settings from ground stations. Where else
> would they come from?

You get them off DUATS like the rest of us?

Roy Smith wrote:
> In article >,
> Newps > wrote:
>
>
>>John R. Copeland wrote:
>>
>>
>>>Chip, you didn't mention enroute altimeter settings being different from
>>>surface ones.
>>>I've seen that condition in the Rocky Mountains, but I can't specifically
>>>recall
>>>if I've ever seen it in the central and eastern U.S.
>>
>>Controllers issue altimeter settings from ground stations. Where else
>>would they come from?
>
>
> You get them off DUATS like the rest of us?

Yes, and they come from ground stations. There are no special enroute
airborne stations in the mountains.

I fail to see what the usefulness would be.

As long as everyone is flying with the same lapse rate error, who
cares?




On Mon, 04 Apr 2005 08:12:04 -0600, Newps > wrote:

>
>
>Roy Smith wrote:
>> In article >,
>> Newps > wrote:
>>
>>
>>>John R. Copeland wrote:
>>>
>>>
>>>>Chip, you didn't mention enroute altimeter settings being different from
>>>>surface ones.
>>>>I've seen that condition in the Rocky Mountains, but I can't specifically
>>>>recall
>>>>if I've ever seen it in the central and eastern U.S.
>>>
>>>Controllers issue altimeter settings from ground stations. Where else
>>>would they come from?
>>
>>
>> You get them off DUATS like the rest of us?
>
>Yes, and they come from ground stations. There are no special enroute
>airborne stations in the mountains.

"Newps" > wrote in message =
...
>=20
>=20
> Roy Smith wrote:
>> In article >,
>> Newps > wrote:
>>=20
>>=20
>>>John R. Copeland wrote:
>>>
>>>
>>>>Chip, you didn't mention enroute altimeter settings being different =
from=20
>>>>surface ones.
>>>>I've seen that condition in the Rocky Mountains, but I can't =
specifically=20
>>>>recall
>>>>if I've ever seen it in the central and eastern U.S.
>>>
>>>Controllers issue altimeter settings from ground stations. Where =
else=20
>>>would they come from?
>>=20
>>=20
>> You get them off DUATS like the rest of us?
>=20
> Yes, and they come from ground stations. There are no special enroute =

> airborne stations in the mountains.

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.
The terminology I've heard used at specific locations is something like:
"XXX altimeter nn.nn, Area altimeter nn.mm."
I don't really know how the "Area" numbers are established,
but I'd certainly want to use the local airport setting for landings.

"John R. Copeland" > wrote in message
...
>
> 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.
> The terminology I've heard used at specific locations is something like:
> "XXX altimeter nn.nn, Area altimeter nn.mm."
> I don't really know how the "Area" numbers are established,
> but I'd certainly want to use the local airport setting for landings.
>

Where did you hear "area altimeter nn.nn"?

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

> 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.

How would a station be more representative if it was/wasn't in a valley or
on a hill top?

"Steven P. McNicoll" > wrote in message =
. net...
>=20
> "John R. Copeland" > wrote in message=20
> ...
>>
>> 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.
>> The terminology I've heard used at specific locations is something =
like:
>> "XXX altimeter nn.nn, Area altimeter nn.mm."
>> I don't really know how the "Area" numbers are established,
>> but I'd certainly want to use the local airport setting for landings.
>>
>=20
> Where did you hear "area altimeter nn.nn"?
>

One place I recall specifically was KBCE.

"Matt Barrow" > wrote in message =
...
>=20
> "John R. Copeland" > wrote in message
> ...
>=20
>> 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.
>=20
> How would a station be more representative if it was/wasn't in a =
valley or
> on a hill top?
>=20
>

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.

"John R. Copeland" > wrote in message
...
"Steven P. McNicoll" > wrote in message
. net...
>
> "John R. Copeland" > wrote in message
> ...
>>
>> 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.
>> The terminology I've heard used at specific locations is something like:
>> "XXX altimeter nn.nn, Area altimeter nn.mm."
>> I don't really know how the "Area" numbers are established,
>> but I'd certainly want to use the local airport setting for landings.
>>
>
> Where did you hear "area altimeter nn.nn"?
>

One place I recall specifically was KBCE.

"John R. Copeland" > wrote in message
...
>
> One place I recall specifically was KBCE.
>

The controller issued the Bryce Canyon altimeter and the "area" altimeter?
Did you happen to ask him how he determined the "area" altimeter?

Roy Smith wrote:

>"O. Sami Saydjari" > wrote:
>
>
>>So are we are concluding that it is best to switch to ATC altimeter
>>setting as soon as they give them to you
>>
>>
>
>That's what I'm concluding. You?
>
>
>
>>and that differences from local airport settings, except when you are on
>>approach to your destination (where you use that airport's setting).
>>
>>
>
>I'll always favor an altimeter setting ATC gives me over anything I hear on
>the ATIS. The ATIS could be up to an hour old; the controller is looking
>at the most current reading right now.
>
>
And you do not think the controller is getting his information as
reported by that station's ATIS / AWOS/ ETC?

Ross

"Roy Smith" > wrote in message
...
>
> I'll always favor an altimeter setting ATC gives me over anything I hear
> on
> the ATIS. The ATIS could be up to an hour old; the controller is looking
> at the most current reading right now.
>

Which could also be up to an hour old.

"Steven P. McNicoll" > wrote in message =
k.net...
>=20
> "John R. Copeland" > wrote in message=20
> ...
>>
>> One place I recall specifically was KBCE.
>>
>=20
> The controller issued the Bryce Canyon altimeter and the "area" =
altimeter?=20
> Did you happen to ask him how he determined the "area" altimeter?
>

It wasn't a controller, it was an FSS specialist, and sadly I asked him =
only
what the "area setting" meant, not how he determined it.
Since nobody here seems to know about it, it may be one of those things
no longer in use. It seemed reasonable to me at the time, though.

"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.

"John R. Copeland" > wrote in message
...
>
> It wasn't a controller, it was an FSS specialist,
>

You said previously it was ATC.


>
> and sadly I asked him only
> what the "area setting" meant, not how he determined it.
> Since nobody here seems to know about it, it may be one of those things
> no longer in use. It seemed reasonable to me at the time, though.
>

I doubt it was ever in use.

"Steven P. McNicoll" > wrote in message =
k.net...
>=20
> "John R. Copeland" > wrote in message
> ...
>>
>> It wasn't a controller, it was an FSS specialist,
>>
>=20
> You said previously it was ATC.
>=20

Yes I did, but I absolutely mis-spoke. Sorry.

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.

"Matt Barrow" > wrote in message
...
>
> "John R. Copeland" > wrote in message
> ...
>
>> 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.
>
> How would a station be more representative if it was/wasn't in a valley or
> on a hill top?
>
>

This is an obstruction-clearance issue in very cold weather.

If the altimeter setting came from a station in the valley 5000 feet in true
height below the aircraft, the indicated height could differ from true
height by as much as 1500 feet feet.

If it came from a station on the hill only 1000 feet in true height from the
aircraft, the difference is likely less than 300 feet. (Source: Canadian
AIP)

If you are choosing flight altitudes without much margin for obstacle
clearance, you may want to ask for somewhat higher altitudes if you will be
using settings from valley stations.

"Icebound" > wrote in message
...
> > How would a station be more representative if it was/wasn't in a valley
or
> > on a hill top?
> >
> >
>
> This is an obstruction-clearance issue in very cold weather.
>
> If the altimeter setting came from a station in the valley 5000 feet in
true
> height below the aircraft, the indicated height could differ from true
> height by as much as 1500 feet feet.
>
> If it came from a station on the hill only 1000 feet in true height from
the
> aircraft, the difference is likely less than 300 feet. (Source: Canadian
> AIP)
>
> If you are choosing flight altitudes without much margin for obstacle
> clearance, you may want to ask for somewhat higher altitudes if you will
be
> using settings from valley stations.
>

Mind telling me how that variation (of that magnitude) could come about?

"Matt Barrow" > wrote in message
...
>
> "Icebound" > wrote in message
> ...
>> > How would a station be more representative if it was/wasn't in a valley
> or
>> > on a hill top?
>> >
>> >
>>
>> This is an obstruction-clearance issue in very cold weather.
>>
>> If the altimeter setting came from a station in the valley 5000 feet in
> true
>> height below the aircraft, the indicated height could differ from true
>> height by as much as 1500 feet feet.
>>
>> If it came from a station on the hill only 1000 feet in true height from
> the
>> aircraft, the difference is likely less than 300 feet. (Source: Canadian
>> AIP)
>>
>> If you are choosing flight altitudes without much margin for obstacle
>> clearance, you may want to ask for somewhat higher altitudes if you will
> be
>> using settings from valley stations.
>>
>
> Mind telling me how that variation (of that magnitude) could come about?
>
>

Its been discussed here many times, but I will review:

We know that an altimeter setting by definition means that, set to the
station-determined value, our INDICATED altitude will match the REAL
ELEVATION, when we are parked on the threshold of the station. Bascially,
the "altimeter setting" which we set in the Kollsman window, is what
accomplishes that correction-for-station-elevation, so that we get MSL and
our INDICATED readout.

Beyond that, when we fly at some indicated altitude other than that exactly
equal to the station's, we are following a constant air pressure... a
pressure which is some fixed amount LESS (if we are higher) than the actual
air pressure at our station. The altimeter, converts this
pressure-difference (between the pressure at the station, and the actual
pressure at the airplane)... into an altitude readout. Adjusted, of course,
by adding the elevation of the station to get MSL... as I have already
mentioned, by means of the altimeter-setting adjustment.

But because the altimeter has no knowledge of the ambient temperature, it
makes this pressure-difference conversion assuming the "standard"
atmosphere. In our very cold conditions, the air is much denser that the
"standard", and thus the pressure levels are much closer together... in
other words: as we climb away from the altimeter-setting-station, the
pressure decreases much more, in 1000 feet of REAL altitude, than it does in
"standard" temperature conditions. Therefore our altimeter will read higher
than the REAL altitude, because it only knows about the lower pressure, and
nothing about the colder temperature. The altimeter reads higher than real,
real elevation is lower than indicataed, obstruction clearance may be an
issue.

Naturally, the further we climb from our altimeter-setting-station, the
greater the error. That is why we can reduce this error if we can get the
altimeter setting from the station closest to our real altitude.

Remember that this has nothing to do with assigned altitudes. Those are
flown according to the INDICATED altitude whatever it happens to be, based
on whatever approved official altimeter setting you have. The Canadian rules
specifically say:

quote:
IFR assigned altitudes accepted by a pilot shall not be adjusted to
compensate for cold
temperatures, i.e., if a pilot accepts “maintain 3 000”, an altitude
correction shall not be
applied to 3 000 ft.
:unquote

BUT IF there a concern about clearing obstacles or terrain, a knowledge of
the probable error between indicated and actual may cause you to file and/or
request a higher INDICATED altitude.

The actual numbers can be calculated from knowledge of "air constants", and
temperature-density relationships, etc., but since we fly in very cold
weather up here quite a bit, Transport Canada has done the math and
published some figures for us in the Canadian equivalent of the AIM.

Fore example, at 40 below, 5000 feet away from altimeter-setting-station,
error is published as 1210 feet. At 50 below it is 1500 feet. 1000 feet
away from altimeter-setting-station, error is published as 240 feet at 40
below, 300 feet at 50...

The comment is often made: "Well if the air is cold, and cold air is dense,
then the pressure that I am flying at should be higher", and not lower as I
have shown above. But that statement ignores the fact that air is
compressible and thus more of that cold density is BELOW you. The pressure
at your altitude is produced only by the weight of the air ABOVE you.

"Matt Barrow" > writes:

> "Icebound" > wrote:
> [...]
> > If the altimeter setting came from a station in the valley 5000 feet in
> > true height below the aircraft, the indicated height could differ from true
> > height by as much as 1500 feet feet.
> >
> > If it came from a station on the hill only 1000 feet in true height from
> > the aircraft, the difference is likely less than 300 feet. [...]
>
> Mind telling me how that variation (of that magnitude) could come about?

If you run through the full "true altitude" calculation discussed
during early ground school, you'll see that there is a term that
relates to the elevation of the measurement station. The effect
is that the lower you are AGL, the closer the calibrated & true
altitudes tend to become, because deviations from the standard
atmosphere become less significant within less tall columns of air.

- FChE

"Frank Ch. Eigler" > wrote in message
...
>
> "Matt Barrow" > writes:
>
> > "Icebound" > wrote:
> > [...]
> > > If the altimeter setting came from a station in the valley 5000 feet
in
> > > true height below the aircraft, the indicated height could differ from
true
> > > height by as much as 1500 feet feet.
> > >
> > > If it came from a station on the hill only 1000 feet in true height
from
> > > the aircraft, the difference is likely less than 300 feet. [...]
> >
> > Mind telling me how that variation (of that magnitude) could come about?
>
> If you run through the full "true altitude" calculation discussed
> during early ground school, you'll see that there is a term that
> relates to the elevation of the measurement station. The effect
> is that the lower you are AGL, the closer the calibrated & true
> altitudes tend to become, because deviations from the standard
> atmosphere become less significant within less tall columns of air.

Ground stations are all AT GROUND LEVEL, whether the station is at 2000 MSL
or 6000 MSL.

"Icebound" > wrote in message
...
>
> "Matt Barrow" > wrote in message
> ...
> >
> > "Icebound" > wrote in message
> > ...
> >> > How would a station be more representative if it was/wasn't in a
valley
> > or
> >> > on a hill top?
> >> >
> >> >
> >>
> >> This is an obstruction-clearance issue in very cold weather.
> >>
> >> If the altimeter setting came from a station in the valley 5000 feet in
> > true
> >> height below the aircraft, the indicated height could differ from true
> >> height by as much as 1500 feet feet.
> >>
> >> If it came from a station on the hill only 1000 feet in true height
from
> > the
> >> aircraft, the difference is likely less than 300 feet. (Source:
Canadian
> >> AIP)
> >>
> >> If you are choosing flight altitudes without much margin for obstacle
> >> clearance, you may want to ask for somewhat higher altitudes if you
will
> > be
> >> using settings from valley stations.
> >>
> >
> > Mind telling me how that variation (of that magnitude) could come
about?
> >
> >
>
> Its been discussed here many times, but I will review:
>
> We know that an altimeter setting by definition means that, set to the
> station-determined value, our INDICATED altitude will match the REAL
> ELEVATION, when we are parked on the threshold of the station. Bascially,
> the "altimeter setting" which we set in the Kollsman window, is what
> accomplishes that correction-for-station-elevation, so that we get MSL and
> our INDICATED readout.
>
> Beyond that, when we fly at some indicated altitude other than that
exactly
> equal to the station's, we are following a constant air pressure... a
> pressure which is some fixed amount LESS (if we are higher) than the
actual
> air pressure at our station. The altimeter, converts this
> pressure-difference (between the pressure at the station, and the actual
> pressure at the airplane)... into an altitude readout. Adjusted, of
course,
> by adding the elevation of the station to get MSL... as I have already
> mentioned, by means of the altimeter-setting adjustment.
>
> But because the altimeter has no knowledge of the ambient temperature, it
> makes this pressure-difference conversion assuming the "standard"
> atmosphere. In our very cold conditions, the air is much denser that the
> "standard", and thus the pressure levels are much closer together... in
> other words: as we climb away from the altimeter-setting-station, the
> pressure decreases much more, in 1000 feet of REAL altitude, than it does
in
> "standard" temperature conditions. Therefore our altimeter will read
higher
> than the REAL altitude, because it only knows about the lower pressure,
and
> nothing about the colder temperature. The altimeter reads higher than
real,
> real elevation is lower than indicataed, obstruction clearance may be an
> issue.
>
> Naturally, the further we climb from our altimeter-setting-station, the
> greater the error. That is why we can reduce this error if we can get the
> altimeter setting from the station closest to our real altitude.
>
> Remember that this has nothing to do with assigned altitudes. Those are
> flown according to the INDICATED altitude whatever it happens to be, based
> on whatever approved official altimeter setting you have. The Canadian
rules
> specifically say:
>
> quote:
> IFR assigned altitudes accepted by a pilot shall not be adjusted to
> compensate for cold
> temperatures, i.e., if a pilot accepts “maintain 3 000”, an altitude
> correction shall not be
> applied to 3 000 ft.
> :unquote
>
> BUT IF there a concern about clearing obstacles or terrain, a knowledge of
> the probable error between indicated and actual may cause you to file
and/or
> request a higher INDICATED altitude.
>
> The actual numbers can be calculated from knowledge of "air constants",
and
> temperature-density relationships, etc., but since we fly in very cold
> weather up here quite a bit, Transport Canada has done the math and
> published some figures for us in the Canadian equivalent of the AIM.
>
> Fore example, at 40 below, 5000 feet away from altimeter-setting-station,
> error is published as 1210 feet. At 50 below it is 1500 feet. 1000 feet
> away from altimeter-setting-station, error is published as 240 feet at 40
> below, 300 feet at 50...
>
> The comment is often made: "Well if the air is cold, and cold air is
dense,
> then the pressure that I am flying at should be higher", and not lower as
I
> have shown above. But that statement ignores the fact that air is
> compressible and thus more of that cold density is BELOW you. The
pressure
> at your altitude is produced only by the weight of the air ABOVE you.
>
>

You're bringing in a lot of irrelevant material. The original point was
"Area" altmiter settings and another point made that a station in
mountainous areas would be more accurate if it was located on the mountain
top at higher altitude than a station at lower altitude in the same area.

You're still not explaining how a ground station at, say, 6000' MSL would
be have a more accurate baro reading than one down in a nearby valley at,
say, 2000' MSL. That is the point of the thread.

The way I see it, if you have two stations, one on the ground at 350
feet MSL, and the other on the ground (on top of a mountain) at 5000
feet MSL, and they are both "nearby", then the one that is actually at
5000 feet MSL will give an altimeter setting that will be more accurate
for an airplane that's flying at 5000 feet MSL.

The altimeter setting from the 350' station will be correct at that 350'
elevation, but the altitude indicated by using that setting in the
window will be a guess (based on standard lapse rate and other such) for
an airplane at 5000 feet. Granted, usually a pretty good guess, but
altimeter altitude is still an indirect inference from other parameters
(pressure and such). If the actual atmosphere that day does not follow
the theoretical average curves, the actual altitude of an airplane that
is indicating 5000 feet using an altimeter setting from 350' will be
somewhat off.

Of course, the airplane that uses the 5000' station's altimeter setting
while at 5000 feet, and proceeds to land at the 350' high airstrip, will
likely find the indicated altitude once on the ground to be different
from 350' (by about the same amount)

Given this, it makes sense to me (depending on the accuracy needed and
the actual difference from standard lapse rate) that flights =through=
an area might use one setting, and flights =to= an area might use
another one - at least when setting up to land.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

"Matt Barrow" > writes:

> [i]
> > If you run through the full "true altitude" calculation discussed
> > during early ground school, you'll see that there is a term that
> > relates to the elevation of the measurement station. [...]
>
> Ground stations are all AT GROUND LEVEL, whether the station is at
> 2000 MSL or 6000 MSL.

That's quite insightful, but irrelevant to the issue of *elevation* of
those stations.

- FChE

"Jose" > wrote in message
om...
> The way I see it, if you have two stations, one on the ground at 350
> feet MSL, and the other on the ground (on top of a mountain) at 5000
> feet MSL, and they are both "nearby", then the one that is actually at
> 5000 feet MSL will give an altimeter setting that will be more accurate
> for an airplane that's flying at 5000 feet MSL.

How?

>
> The altimeter setting from the 350' station will be correct at that 350'
> elevation, but the altitude indicated by using that setting in the
> window will be a guess (based on standard lapse rate and other such) for
> an airplane at 5000 feet. Granted, usually a pretty good guess, but
> altimeter altitude is still an indirect inference from other parameters
> (pressure and such). If the actual atmosphere that day does not follow
> the theoretical average curves, the actual altitude of an airplane that
> is indicating 5000 feet using an altimeter setting from 350' will be
> somewhat off.

Ummmm...air pressure is constant when corrected for altitude. otherwise they
would give altimeter setttings at various altitude, not a various locations.

> Of course, the airplane that uses the 5000' station's altimeter setting
> while at 5000 feet, and proceeds to land at the 350' high airstrip, will
> likely find the indicated altitude once on the ground to be different
> from 350' (by about the same amount)

Might you be able to point me to a difinitive paper on that rather than just
idle specualtion?

> Given this, it makes sense to me (depending on the accuracy needed and
> the actual difference from standard lapse rate) that flights =through=
> an area might use one setting, and flights =to= an area might use
> another one - at least when setting up to land.

Again, could you point me to an authoritative reference?

I keep hearing people running on about that they would be different, but
nothing substantial offered as evidence and certainly nothing I've heard of
in 25 years of flying (but I might have had a deprived career).

--
Matt
---------------------
Matthew W. Barrow
Site-Fill Homes, LLC.
Montrose, CO

"Frank Ch. Eigler" > wrote in message
...
>
> "Matt Barrow" > writes:
>
> > [i]
> > > If you run through the full "true altitude" calculation discussed
> > > during early ground school, you'll see that there is a term that
> > > relates to the elevation of the measurement station. [...]

Which has nothing to do with how accurate they would be -- it's all
corrected out.

> >
> > Ground stations are all AT GROUND LEVEL, whether the station is at
> > 2000 MSL or 6000 MSL.
>
> That's quite insightful, but irrelevant to the issue of *elevation* of
> those stations.

Which you haven't answered either...or any of the other four or five people
who've responded. Only the same "well, maybe it might be....".

"Matt Barrow" > wrote in message
...
>
>
> You're bringing in a lot of irrelevant material. The original point was
> "Area" altmiter settings and another point made that a station in
> mountainous areas would be more accurate if it was located on the mountain
> top at higher altitude than a station at lower altitude in the same area.
>
> You're still not explaining how a ground station at, say, 6000' MSL would
> be have a more accurate baro reading than one down in a nearby valley at,
> say, 2000' MSL. That is the point of the thread.
>
>
>


There is NO issue of "altimeter-setting accuracy" nor "barometer accuracy".

Both stations have accurate barometers, and are reading their station
pressure correctly and accurately. Both altimeter-settings are "accurate"
in so far as the settings have been properly determined according to the
rules, for each individual station's actual-air-pressure and each individual
station's actual-measured-elevation.

But as we all know, setting our altimeter to an "accurate altimeter setting"
does not mean that the INDICATED altitude matches the TRUE altitude. In
almost never ever does, because the real atmosphere is almost always
different from the "standard" for which altimeters are calibrated.

So there is always a discrepancy between INDICATED and TRUE altitudes. In
most cases this does not matter, because the discrepancy is the same for
everybody.

Somebody in this thread asked WHY this discrepancy was greater if using a
valley station's setting, as opposed to a hill station's setting. (He may
have used the word "accuracy", but his meaning was: "why is my INDICATED
altitude going to be closer to my TRUE altitude when I use the
hill-station's-altimeter setting as opposed to the valley's?")

My entire tirade was to try to explain why that is so... and just to warn,
that in very cold weather, this means that you are flying much lower (TRUE
altitude) than INDICATED. If you are not paying attention to
indicated-vs-true discrepancies, you may choose an INDICATED altitude which
may put you below a comfortable margin of terrain/obstacle clearance.

"Matt Barrow" > wrote in message
...
>
> "Frank Ch. Eigler" > wrote in message
> ...
>>
>> "Matt Barrow" > writes:
>>
>> > "Icebound" > wrote:
>> > [...]
>> > > If the altimeter setting came from a station in the valley 5000 feet
> in
>> > > true height below the aircraft, the indicated height could differ
>> > > from
> true
>> > > height by as much as 1500 feet feet.
>> > >
>> > > If it came from a station on the hill only 1000 feet in true height
> from
>> > > the aircraft, the difference is likely less than 300 feet. [...]
>> >
>> > Mind telling me how that variation (of that magnitude) could come
>> > about?
>>
>> If you run through the full "true altitude" calculation discussed
>> during early ground school, you'll see that there is a term that
>> relates to the elevation of the measurement station. The effect
>> is that the lower you are AGL, the closer the calibrated & true
>> altitudes tend to become, because deviations from the standard
>> atmosphere become less significant within less tall columns of air.
>
> Ground stations are all AT GROUND LEVEL, whether the station is at 2000
> MSL
> or 6000 MSL.

Ground stations are all more or less at ground level. But they report
their
altimeter settings in terms of Mean Sea Level, in order to provide a common
basis of comparison. This means that the air pressure read from the
station's
barometer must be *corrected* to sea level. The correction is in terms of
the conditions of the ICAO standard atmosphere, taking account the
difference
in elevation from MSL only: i.e. temperature, humidity etc. or other local
differences in the composition of the atmosphere are not considered in this
correction.

An altimeter can be expected to indicate the correct altitude (+/- 75') only
on the ground at the given ground station, and elsewhere, only where ICAO
standard conditions prevail. For any other position or condition the
altimeter
can be expected to be in error (and the atmosphere can be expected to
always
differ from the ICAO standard conditions).

For positions directly above or below the given station, the amount of
error can be expected to be roughly proportional to the difference between
the actual altitude and the station elevation.

Thus, for a flight at 5000 feet, the altimeter setting for a (nearby) ground
station at 5000 feet elevation can be expected to indicate closer to true
altitude than when using the altimieter setting for a station at sea level.
For a flight nearer sea level, the setting from the (nearby) sea level
station
will indicate closer to the true altitude than the altimeter setting for the
5000'
station.

In either case, there can be expected to be other errors due to the lateral
distance to the station as well, and the difference in atmospheric
conditions
that this entails.

The desire to minimize these effects is why we generally choose the
altimeter
setting from the nearest ground station, or otherwise nearest to our route
of
flight. And why, in the point under discussion, a nearby ground station
located
nearer to our actual altitude is better than one at a different elevation.

"Icebound" > wrote in message
...
>
> "Matt Barrow" > wrote in message
> ...
> >
> >
> > You're bringing in a lot of irrelevant material. The original point was
> > "Area" altmiter settings and another point made that a station in
> > mountainous areas would be more accurate if it was located on the
mountain
> > top at higher altitude than a station at lower altitude in the same
area.
> >
> > You're still not explaining how a ground station at, say, 6000' MSL
would
> > be have a more accurate baro reading than one down in a nearby valley
at,
> > say, 2000' MSL. That is the point of the thread.
> >
> >
> >
>
>
> There is NO issue of "altimeter-setting accuracy" nor "barometer
accuracy".
>
> Both stations have accurate barometers, and are reading their station
> pressure correctly and accurately. Both altimeter-settings are "accurate"
> in so far as the settings have been properly determined according to the
> rules, for each individual station's actual-air-pressure and each
individual
> station's actual-measured-elevation.
>
> But as we all know, setting our altimeter to an "accurate altimeter
setting"
> does not mean that the INDICATED altitude matches the TRUE altitude. In
> almost never ever does, because the real atmosphere is almost always
> different from the "standard" for which altimeters are calibrated.
>
> So there is always a discrepancy between INDICATED and TRUE altitudes. In
> most cases this does not matter, because the discrepancy is the same for
> everybody.
>
> Somebody in this thread asked WHY this discrepancy was greater if using a
> valley station's setting, as opposed to a hill station's setting. (He may
> have used the word "accuracy", but his meaning was: "why is my INDICATED
> altitude going to be closer to my TRUE altitude when I use the
> hill-station's-altimeter setting as opposed to the valley's?")

No, he claimed that ATC uses mountain top reporting stations rather than
lower level ones for "area settings". That makes two fallacies in one post.

>
> My entire tirade was to try to explain why that is so... and just to warn,
> that in very cold weather, this means that you are flying much lower (TRUE
> altitude) than INDICATED. If you are not paying attention to
> indicated-vs-true discrepancies, you may choose an INDICATED altitude
which
> may put you below a comfortable margin of terrain/obstacle clearance.

In cold weather, then, it doesn't matter much which reporting station is
used _if pilots don't make necessary corrections for True Altitude_. Same
thing for the other side of the coin, not correcting for density altitude.
Does ATC use valley reporting stations in the summer then?

"Ron McKinnon" > wrote in message
news:f8W4e.916805$8l.223757@pd7tw1no...
>
> An altimeter can be expected to indicate the correct altitude (+/- 75')
only
> on the ground at the given ground station, and elsewhere, only where ICAO
> standard conditions prevail. For any other position or condition the
> altimeter
> can be expected to be in error (and the atmosphere can be expected to
> always
> differ from the ICAO standard conditions).

Well, if there is a valley reporting station and nearby mountain top
station, ICAO conditions are not likely to be met in either instance.

> The desire to minimize these effects is why we generally choose the
altimeter
> setting from the nearest ground station, or otherwise nearest to our route
of
> flight.

True, but the point made was that ATC uses higher altitude reporting
stations as "they are more accurate".

> And why, in the point under discussion, a nearby ground station located
> nearer to our actual altitude is better than one at a different elevation.

Yes, an "area setting" :>)

"Matt Barrow" > wrote in message
...
>
> In cold weather, then, it doesn't matter much which reporting station is
> used _if pilots don't make necessary corrections for True Altitude_.

It matters only because, for the pilot who DID NOT make the necessary
mental adjustment, the discrepancy between indicated and actual altitude
will be GREATER when using the lower-elevation setting, and hence the
possibility of choosing an inappropriate flight altitude (indicate) is also
greater.


> Same thing for the other side of the coin, not correcting for density
> altitude.
> Does ATC use valley reporting stations in the summer then?
>

It has been repeated in this thread several times:
"The greater the difference in elevation between your aircraft and your
altimeter-setting-station, the GREATER THE DISCREPANCY BETWEEN INDICATED AND
TRUE ALTITUDE."

This is true in ALL cases, cold and hot. In hot weather, the discrepancy
will be in the opposite direction (TRUE altitude will be HIGHER than
INDICATED altitude), but the absolute value of the discrepancy will still be
GREATER when using the valley station.

>>The way I see it, if you have two stations, one on the ground at 350
>> feet MSL, and the other on the ground (on top of a mountain) at 5000
>> feet MSL, and they are both "nearby", then the one that is actually at
>> 5000 feet MSL will give an altimeter setting that will be more accurate
>> for an airplane that's flying at 5000 feet MSL.
>
> How?

One way to get an altimeter setting is to put an altimeter at the
station, and twist the dial until the actual altitude is shown, and then
read the window. If the station is =at= 5000 feet MSL, then (assuming
horizontal uniformity over the distances involved), any altimeter using
this setting will show an alititude of 5000 feet when they are at the
same altitude as the station. An airplane at 5000 feet using this
setting will show an altitude of 5000 feet.

The station that is physically located at 350 feet MSL would twist the
dial until 350 MSL shows up, and then read the window. IN A STANDARD
ATMOSPHERE, the number in the window should be the same as the one at
the 5000' station. But if the atmosphere is other than standard, the
number in the window (the altimeter setting) will be different. So the
airplane that is using =that= setting, and indicating 5000', will be at
a different altitude from the one using the 5000' station, and also
indicating 5000'. We already know the aircraft using the 5000'
station's setting is dead on, so the other aircraft is off.

> Ummmm...air pressure is constant when corrected for altitude. otherwise they
> would give altimeter setttings at various altitude, not a various locations.

The correction for altitude presumes a standard atmosphere. When the
atmosphere is nonstandard, this doesn't apply any more.

>>Of course, the airplane that uses the 5000' station's altimeter setting
>> while at 5000 feet, and proceeds to land at the 350' high airstrip, will
>> likely find the indicated altitude once on the ground to be different
>> from 350' (by about the same amount)
>
> Might you be able to point me to a difinitive paper on that rather than just
> idle specualtion?

No.

> I keep hearing people running on about that they would be different, but
> nothing substantial offered as evidence and certainly nothing I've heard of
> in 25 years of flying (but I might have had a deprived career).

Any book on flying, altimeters, and weather, should have a section on
how altimeters guess altitude based on pressure, and the assumptions
that are made in order to do so. Those books will refer to the
"Standard atmosphere", which includes formulas for how air pressure,
temerature, and humidity are presumed to change with altitude. Look up
the "high to low, look out below" rule; it's based on the same idea, and
in the discussion of the origins of this rule of thumb, you should come
across (in print) the same things we are discussing here, and with the
imprimateur of the author of the book.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

"Matt Barrow" > writes:

> [...]
> > The desire to minimize these effects is why we generally choose the
> > altimeter setting from the nearest ground station, or otherwise
> > nearest to our route of flight.
>
> True, but the point made was that ATC uses higher altitude reporting
> stations as "they are more accurate".
> [...]

Matt, you're continuing to pick silly nits instead of showing a
willingness to understand the issue. The higher stations are more
accurate in the clearly stated sense of causing indicated altitudes to
be closer to true altitude. Please stop asking for repeated
elaboration, or attempt historical revision, and just work through
some ground school exercises on the subject.


- FChE

"Jose" > wrote in message
om...
>
> The way I see it, if you have two stations, one on the ground at 350 feet
> MSL, and the other on the ground (on top of a mountain) at 5000 feet MSL,
> and they are both "nearby", then the one that is actually at 5000 feet MSL
> will give an altimeter setting that will be more accurate for an airplane
> that's flying at 5000 feet MSL.
>

Unless that airplane is taking off or landing it would seem to be below the
minimum IFR altitude.

>>The way I see it, if you have two stations, one on the ground at 350 feet
>> MSL, and the other on the ground (on top of a mountain) at 5000 feet MSL,
>> and they are both "nearby", then the one that is actually at 5000 feet MSL
>> will give an altimeter setting that will be more accurate for an airplane
>> that's flying at 5000 feet MSL.
> Unless that airplane is taking off or landing it would seem to be below the
> minimum IFR altitude.

.... or separated from the station laterally by a "sufficient" distance,
which will usually not be sufficient for lateral differences in air
pressure to have much effect, but could easily be sufficiently distant
for adequate cumulo-granite separation.

And altimeters are useful for VFR flying too.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

"Jose" > wrote in message
m...
>
> ... or separated from the station laterally by a "sufficient" distance,
> which will usually not be sufficient for lateral differences in air
> pressure to have much effect, but could easily be sufficiently distant for
> adequate cumulo-granite separation.
>

The mountain was stated to be "nearby".


>
> And altimeters are useful for VFR flying too.
>

Yes, but we're discussing this in rec.aviation.ifr.

"Frank Ch. Eigler" > wrote in message
...
>
> "Matt Barrow" > writes:
>
> > [...]
> > > The desire to minimize these effects is why we generally choose the
> > > altimeter setting from the nearest ground station, or otherwise
> > > nearest to our route of flight.
> >
> > True, but the point made was that ATC uses higher altitude reporting
> > stations as "they are more accurate".
> > [...]
>
> Matt, you're continuing to pick silly nits instead of showing a
> willingness to understand the issue.

I understand the issue, why don't you stop evading the question?

> The higher stations are more
> accurate in the clearly stated sense of causing indicated altitudes to
> be closer to true altitude. Please stop asking for repeated
> elaboration, or attempt historical revision, and just work through
> some ground school exercises on the subject.

Now why don't you stop evading the original question/point and point me to
where it says ATC uses high altitude reporting stations because of this
known (I know it too) increase in accuracy?

Someone made a boneheaded assertion and everyone missed (except Newps) that
though they would be more accurate, that ATC does not use such stations for
said accuracy.

So instead of picking nits, why not focus on the question instead of
evading.

>>The way I see it, if you have two stations, one on the ground at 350 feet
>> MSL, and the other on the ground (on top of a mountain) at 5000 feet MSL,
>> and they are both "nearby", then the one that is actually at 5000 feet
MSL
>> will give an altimeter setting that will be more accurate for an airplane
>> that's flying at 5000 feet MSL.

Both stations use a corrected reading; it's the altimeter aboard the
aircraft the will need to adjust for temperature, air pressure being
constant.


--
Matt
---------------------
Matthew W. Barrow
Site-Fill Homes, LLC.
Montrose, CO

"Matt Barrow" > wrote in message
...
>
>>>The way I see it, if you have two stations, one on the ground at 350 feet
>>> MSL, and the other on the ground (on top of a mountain) at 5000 feet
>>> MSL,
>>> and they are both "nearby", then the one that is actually at 5000 feet
> MSL
>>> will give an altimeter setting that will be more accurate for an
>>> airplane
>>> that's flying at 5000 feet MSL.

> Both stations use a corrected reading; it's the altimeter aboard the
> aircraft the will need to adjust for temperature, air pressure being
> constant.

.... which suggests you don't.

(Air pressure being constant??? The whole point of the altimeter
is that it isn't, with altitude. What are you trying to say here??)

Though it is true that both station pressures are 'corrected'
which in fact determines their respective altimeter settings,
this is only part of the story.

It is also true that you can 'correct' the indicated altitude
for temperature according to the observed outside air
temperature (and knowing the vertical distance
above or below the ground station from which the
altimeter setting was determined).

But remember that this 'correction', too, is an approximation,
and assumes a particular temperature profile in the
atmosphere between the observation location, and the
reference location.

But there's no way to be assured that that profile is any
more valid than the ICAO Standard Atmosphere that you're
correcting for. And this is only a temperature conversion
- there's no correction available for humidity or other things
that can affect the profile, nor any way in practice to determine
them. So even if you 'correct' for temperature, you can (and
should) still expect the altimeter to be in error.

But the error can generally be expected to be proportional
to the vertical distance between the observation location
(the altimeter) and the reference location (the ground station
from which the altimeter-setting was taken). So if you
reduce this vertical distance, you reduce the error.

Which, again, is why an altimeter setting from a (nearby)
ground station with an closer to your actual altitude
can be expected to produce an indicated altitude
with less error than an altimeter setting from a (nearby)
station that is vertically more distant.

> The mountain was stated to be "nearby".

Like many terms used by the FAA, "nearby" was undefined. I intended it
to be interpreted as near enough so that lateral differences in the
airmass would not be a significant factor, but not so nearby that
collision avoidance becomes dicey, or the ILS takes you underground.
And yes, I know of no ILS installations that actually would take you
underground if flown correctly.

It is possible that critera such as the above are unattainable, for
example the classic security dilemma we face after 9/11 ("greater than
six but less than four"). However in the case above ("nearby") I
believe that there does exist a range of distance that satisfies the
criteria. To pull a number out of the hat, ten miles laterally comes to
mind.

> Yes, but we're discussing this in rec.aviation.ifr.

The forum in which we discuss something does not alter its truth value.
And IFR can be in VMC.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

"Ron McKinnon" > wrote in message
news:nWn5e.924843$6l.234357@pd7tw2no...
>
> "Matt Barrow" > wrote in message
> ...
> >
> >>>The way I see it, if you have two stations, one on the ground at 350
feet
> >>> MSL, and the other on the ground (on top of a mountain) at 5000 feet
> >>> MSL,
> >>> and they are both "nearby", then the one that is actually at 5000 feet
> > MSL
> >>> will give an altimeter setting that will be more accurate for an
> >>> airplane
> >>> that's flying at 5000 feet MSL.
>
> > Both stations use a corrected reading; it's the altimeter aboard the
> > aircraft the will need to adjust for temperature, air pressure being
> > constant.
>
> ... which suggests you don't.
>
> (Air pressure being constant??? The whole point of the altimeter
> is that it isn't, with altitude. What are you trying to say here??)

Sorry...wrong choice of words...SB "does not oscillate within the column of
air (i.e., it's predictable)".

Funny, after 20 or so replies, no one has answered the original question,
only reprinted the explanation of air pressure from the first week of ground
school.

The original point was that +/- "ATC uses reading front reporting stations
on hill tops, rather than from stations nearby in valleys". Gee, I have
terrain over 13000 feet high just a few miles from here, but they (ATC) use
the Montrose or Grand Junction station readings.

"Matt Barrow" > writes:

> [...]
> Funny, after 20 or so replies, no one has answered the original question,
> [...]
>
> The original point was that +/- "ATC uses reading front reporting
> stations on hill tops, rather than from stations nearby in
> valleys". Gee, I have terrain over 13000 feet high just a few miles
> from here, but they (ATC) use the Montrose or Grand Junction station
> readings.

And what exactly is your question now? Why your local ATC does that?
Maybe there is no more better observation station higher up, even
though that would yield more accurate altitudes there.

As you seem to forget, you doubted this point, and that caused the
bulk of the thread. To quote you: "How would a station be more
representative if it was/wasn't in a valley or on a hill top?", and
"You're still not explaining how a ground station at, say, 6000' MSL
would be have a more accurate baro reading than one down in a nearby
valley at, say, 2000' MSL. That is the point of the thread.".

Maybe for en-route purposes, or with their weather patterns, it tends
to be close enough. Maybe they don't want to issue a separate
altimeter call for people doing approaches into the lower areas. Call
and ask them if you really need to know.


- FChE

"Jose" > wrote in message
om...
>
> Like many terms used by the FAA, "nearby" was undefined. I intended it to
> be interpreted as near enough so that lateral differences in the airmass
> would not be a significant factor, but not so nearby that collision
> avoidance becomes dicey, or the ILS takes you underground. And yes, I know
> of no ILS installations that actually would take you underground if flown
> correctly.
>

"Nearby" means it's located a short distance away. What you intended it to
mean is irrelevant.


>
> The forum in which we discuss something does not alter its truth value.
> And IFR can be in VMC.
>

Minimum IFR altitudes apply to IFR operations without regard to IMC or VMC.

> "Nearby" means it's located a short distance away.

.... and what is "short"? A distance which is nearby?

> What you intended it to mean is irrelevant.

Unless one wants to communicate.

> Minimum IFR altitudes apply to IFR operations without regard to IMC or VMC.

I believe I said that, or something consistant with that.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

"Jose" > wrote in message
. com...
>
> ... and what is "short"? A distance which is nearby?
>

Short is having little length; not long.


>
> Unless one wants to communicate.
>

Wanting to communicate is one thing, having the ability to do so is another.


>
> I believe I said that, or something consistant with that.
>

You're mistaken.

> Short is having little length; not long.

....and what is long? "Not short"?

> Wanting to communicate is one thing, having the ability to do so is another.

One of us lacks that ability. I won't speculate on which one that is.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

"Jose" > wrote in message
m...
>
> ...and what is long? "Not short"?
>

Long is having the greater length of two or the greatest length of several.


>
> One of us lacks that ability.

Correct.


>
> I won't speculate on which one that is.
>

It is you.

"Steven P. McNicoll" > wrote in message
nk.net...
>
> "Jose" > wrote in message
> m...
>>
>> ...and what is long? "Not short"?
>>
>
> Long is having the greater length of two or the greatest length of
> several.
>

Incorrect, that's longer, i.e. there are two long runways but one is
longer than the other, or two short runways with one longer.

Having the greater length of several is "longest".

long longer longest

"Chris" > wrote in message
...
>
> Incorrect, that's longer, i.e. there are two long runways but one is
> longer than the other, or two short runways with one longer.
>

Wouldn't the longer of the two be the long one?


>
> Having the greater length of several is "longest".
>
> long longer longest

They're not my definitions, your argument is with a dictionary.

> Long is having the greater length of two or the greatest length of several.

No, it isn't.

> It is you.

Apparantly not.

Followups to alt.definitions and rec.english and misc.oumunications

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

"Jose" > wrote in message
...
>
> No, it isn't.
>

According to dictionaries it is. Why don't you tell the dictionary
producers they're wrong?


>
> Apparantly not.
>

It clearly is.

"Steven P. McNicoll" > wrote in message
ink.net...
>
> "Chris" > wrote in message
> ...
>>
>> Incorrect, that's longer, i.e. there are two long runways but one is
>> longer than the other, or two short runways with one longer.
>>
>
> Wouldn't the longer of the two be the long one?

Nope the longer of the two would be the longer one. They could both be long
ones, but only one can be longer.

"Chris" > wrote in message
...
>
> Nope the longer of the two would be the longer one. They could both be
> long ones, but only one can be longer.
>

Then the dictionary producers got it wrong. Perhaps you'd like to inform
them?

"Steven P. McNicoll" > wrote in message
ink.net...
>
> "Chris" > wrote in message
> ...
>>
>> Nope the longer of the two would be the longer one. They could both be
>> long ones, but only one can be longer.
>>
>
> Then the dictionary producers got it wrong. Perhaps you'd like to inform
> them?

get an English dictionary

"Chris" > wrote in
:

>
> "Steven P. McNicoll" > wrote in message
> ink.net...
>>
>> "Chris" > wrote in message
>> ...
>>>
>>> Incorrect, that's longer, i.e. there are two long runways but
>>> one is longer than the other, or two short runways with one longer.
>>>
>>
>> Wouldn't the longer of the two be the long one?
>
> Nope the longer of the two would be the longer one. They could both be
> long ones, but only one can be longer.

The longer of the two could still be short. If the longer was only 500',
I would still call that short. It's longer, but short. Or you could say
the other one was the shorter one. But you don't have to call me Ray.

--
Regards,

Stan

"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." B. Franklin

One is subjective, the other is objective. What some people think is
long, others would say is short. Longer or longest can be measured,
howeever.

Some people would say this thread is long. Some would even say too
long.

It is certainly longer than it needs to be, and a shorter thread would
have been bettter.

But it's not the longest thread I've ever seen, nor is it certainly
the shortest.

But then, my memory is short. I often wish it were longer.




On 11 Apr 2005 06:15:53 GMT, Stan Gosnell > wrote:

>"Chris" > wrote in
:
>
>>
>> "Steven P. McNicoll" > wrote in message
>> ink.net...
>>>
>>> "Chris" > wrote in message
>>> ...
>>>>
>>>> Incorrect, that's longer, i.e. there are two long runways but
>>>> one is longer than the other, or two short runways with one longer.
>>>>
>>>
>>> Wouldn't the longer of the two be the long one?
>>
>> Nope the longer of the two would be the longer one. They could both be
>> long ones, but only one can be longer.
>
>The longer of the two could still be short. If the longer was only 500',
>I would still call that short. It's longer, but short. Or you could say
>the other one was the shorter one. But you don't have to call me Ray.

> wrote in message
...
> Some people would say this thread is long. Some would even say too
> long.
>
> It is certainly longer than it needs to be, and a shorter thread would
> have been bettter.
>
> But it's not the longest thread I've ever seen, nor is it certainly
> the shortest.
>
> But then, my memory is short. I often wish it were longer.
>

Your memory is neither long nor short. Memory has no length. It simply has
purpose, the operation of remembering.

Time, arguably, has length. It is true that memory may be able to operate
only on the recent past time-span, and not on the long past time-span as
well ....but what is worse: even if it can operate on a long past time-span,
that operation may be innacurate.

:-)

On Mon, 11 Apr 2005 09:27:37 -0400, "Icebound"
> wrote:

>Time, arguably, has length. It is true that memory may be able to operate
>only on the recent past time-span, and not on the long past time-span as
>well ....but what is worse: even if it can operate on a long past time-span,
>that operation may be innacurate.


There is no time in a any sense that can be expressed in length.
Time is only a word we use for measuring change.

Things just exist. Just becaause a rock in space has spun around
another rock n times does not imply some "length".

You are not older than you were 30 years ago. Your cellular structure
has simply changed.

--
*** A great civilization is not conquered from without until it
has destroyed itself from within. ***
- Ariel Durant 1898-1981

> wrote in message
...
> On Mon, 11 Apr 2005 09:27:37 -0400, "Icebound"
> > wrote:
>
>>Time, arguably, has length. It is true that memory may be able to operate
>>only on the recent past time-span, and not on the long past time-span as
>>well ....but what is worse: even if it can operate on a long past
>>time-span,
>>that operation may be innacurate.
>
>
> There is no time in a any sense that can be expressed in length.
> Time is only a word we use for measuring change.
>
> Things just exist. Just becaause a rock in space has spun around
> another rock n times does not imply some "length".
>
> You are not older than you were 30 years ago. Your cellular structure
> has simply changed.

Time (sic) to re-requote one of the more astute observations in this
sub-thread:

"It is certainly longer than it needs to be, and a shorter thread would
have been better."

:-)