YULspotter
Topic Author
Posts: 122
Joined: Thu Mar 30, 2006 11:47 am

Why Does The Tower Give Out Altimetric Reading

Fri Nov 10, 2006 10:58 am

Hello.

I recently purchased a scanner and have been listening in on the conversions between the tower and pilots of approaching aircraft.

I'd like to know why does the tower call out the altimeter reading to the pilots of approaching aircraft. I had heard it had something to do with verification of the ILS settings but I'm not sure.

Any insights would be appreciated.
Thanks.

YULspotter
 
doug_or
Posts: 3125
Joined: Sat Mar 18, 2000 9:55 am

RE: Why Does The Tower Give Out Altimetric Reading

Fri Nov 10, 2006 11:34 am

The altimeters on the aircraft must be set to local preasure to read correctly. This information is on the ATIS, but when that changes, approach and tower controllers will alert aircraft on frequency to the changes (often times just an updated altimeter setting)
When in doubt, one B pump off
 
boeingfixer
Posts: 573
Joined: Fri Jul 29, 2005 2:02 am

RE: Why Does The Tower Give Out Altimetric Reading

Fri Nov 10, 2006 11:39 am

Hi YULspotter,

The reason for giving out the altimeter setting is due to the fact that weather is not static. As high and low pressure systems come and go an altimeter needs to be corrected to sea level to indicate field elevation at that time. Otherwise the altimeters would indicate either higher or lower than field elevation.

Also all aircraft in a control area below transition altitude, FL180 in Canada, have to set their altimeters to the ATC setting. That way all aircraft in the same vicinity are using the same altitude reference. Above transition altitude the altimeters are reset to 29.92 inhg or 1013 millibars.

Cheers, John YYC

[Edited 2006-11-10 03:42:45]

[Edited 2006-11-10 03:44:40]
Cheers, John YYC
 
N231YE
Posts: 2620
Joined: Tue Jul 25, 2006 9:24 am

RE: Why Does The Tower Give Out Altimetric Reading

Fri Nov 10, 2006 12:12 pm

Quoting Boeingfixer (Reply 2):
Also all aircraft in a control area below transition altitude, FL180 in Canada, have to set their altimeters to the ATC setting. That way all aircraft in the same vicinity are using the same altitude reference. Above transition altitude the altimeters are reset to 29.92 inhg or 1013 millibars.

Same thing in the U.S.A. Above 18,000ft, class A airspace begins, and the flight levels begin (beginning at FL180). Upon reaching class A, the altimeter must be set to standard, or 29.92in Hg.

I must also mention, that at uncontrolled airports, pilots are supposed to tune into the ATIS to obtain the altimeter reading, as well as local conditions (Wind Speed, Wind Direction, Cloud Cover, etc).

[Edited 2006-11-10 04:19:10]
 
doug_or
Posts: 3125
Joined: Sat Mar 18, 2000 9:55 am

RE: Why Does The Tower Give Out Altimetric Reading

Fri Nov 10, 2006 12:40 pm

Quoting N231YE (Reply 3):
I must also mention, that at uncontrolled airports, pilots are supposed to tune into the ATIS to obtain the altimeter reading, as well as local conditions (Wind Speed, Wind Direction, Cloud Cover, e

this is true of all airports, not just uncontrolled.
When in doubt, one B pump off
 
boeingfixer
Posts: 573
Joined: Fri Jul 29, 2005 2:02 am

RE: Why Does The Tower Give Out Altimetric Reading

Fri Nov 10, 2006 12:52 pm

Quoting N231YE (Reply 3):
Same thing in the U.S.A. Above 18,000ft, class A airspace begins, and the flight levels begin (beginning at FL180). Upon reaching class A, the altimeter must be set to standard, or 29.92in Hg.

Exactly as I said above in my reply  checkmark 
Cheers, John YYC
 
thegreatchecko
Posts: 689
Joined: Sat Mar 06, 2004 3:34 pm

RE: Why Does The Tower Give Out Altimetric Reading

Fri Nov 10, 2006 1:13 pm

Quoting N231YE (Reply 3):

I must also mention, that at uncontrolled airports, pilots are supposed to tune into the ATIS to obtain the altimeter reading, as well as local conditions (Wind Speed, Wind Direction, Cloud Cover, etc).

Now, because I feel like being picky and this is tech-ops  Smile ...an ATIS (Automatic Terminal Information Service) only exists at a towered airport.

With no tower, its either an ASOS (Automatic Surface Observation System) or AWOS (Automated Weather Observation System) or as I just learned an AWSS (Automated Weather Sensor System).

Without getting too technical, the later three systems observe weather and report it, often changing each transmission.

While the ATIS transmits information, such as weather and runway information, that would congest frequencies at a busier terminal facility and normally do not change more than once an hour. A new one is recorded by the tower each hour unless the weather significantly changes and must be changed. At really large airports, its a creepy robotic voice.

What do you do if the field has no weather reporting? On the ground, set the field elevation into the altimeter. In the air, use the nearest one you can get and keep your eyes out the window so you don't fly into the side of a mountain or tree, the field is VFR only anyways.

For those of you looking for some ATIS humor, here's a link.

Warning, if you are easily offended by language...don't listen!!

MSP ATIS

Checko
"A pilot's plane she is. She will love you if you deserve it, and try to kill you if you don't...She is the Mighty Q400"
 
pilotpip
Posts: 2820
Joined: Fri Sep 19, 2003 3:26 pm

RE: Why Does The Tower Give Out Altimetric Reading

Fri Nov 10, 2006 1:17 pm

Quoting TheGreatChecko (Reply 6):
With no tower, its either an ASOS (Automatic Surface Observation System) or AWOS (Automated Weather Observation System) or as I just learned an AWSS (Automated Weather Sensor System).

I guess that last one is some kind of old-fashioned thingy that they have up there in the great north. How's Alaska treating you bud?
DMI
 
thegreatchecko
Posts: 689
Joined: Sat Mar 06, 2004 3:34 pm

RE: Why Does The Tower Give Out Altimetric Reading

Fri Nov 10, 2006 4:07 pm

They have weather reporting up here????

 bigthumbsup 

Checko
"A pilot's plane she is. She will love you if you deserve it, and try to kill you if you don't...She is the Mighty Q400"
 
redcordes
Posts: 244
Joined: Wed Jan 18, 2006 6:28 am

RE: Why Does The Tower Give Out Altimetric Reading

Fri Nov 10, 2006 8:07 pm

When on an ILS approach, the plates give the altitude at which an aircraft will intercept the Outer Marker if properly on the glideslope. This is a cross-check of the altimeter and the ILS equipment both on the aircraft and the ground. In this day and age with GPS and radio-altimeters, this information is not as necessary as it used to be.
"The only source of knowledge is experience." A. Einstein "Science w/o religion is lame. Religion w/o science is blind."
 
David L
Posts: 8552
Joined: Tue May 18, 1999 2:26 am

RE: Why Does The Tower Give Out Altimetric Reading

Fri Nov 10, 2006 8:22 pm

Quoting TheGreatChecko (Reply 6):
For those of you looking for some ATIS humor, here's a link.

Excellent.  Smile
 
IAHFLYR
Posts: 3943
Joined: Sat Jun 25, 2005 12:56 am

RE: Why Does The Tower Give Out Altimetric Reading

Sat Nov 11, 2006 12:11 am

Quoting TheGreatChecko (Reply 6):
While the ATIS transmits information, such as weather and runway information, that would congest frequencies at a busier terminal facility and normally do not change more than once an hour. A new one is recorded by the tower each hour unless the weather significantly changes and must be changed. At really large airports, its a creepy robotic voice.

All true but also the ATIS gives runway/s in use, approach to expect, pertinent NOTAMS such as closed taxiway etc., so should something as that change as well then a new ATIS is made..........creepy robotic, information OKER!!

Quoting Redcordes (Reply 9):
When on an ILS approach, the plates give the altitude at which an aircraft will intercept the Outer Marker if properly on the glideslope

OM's are going away very quickly, so I'd use the lightning bolt for an altitude cross check as you won't find any OM's at most U.S. airports for much longer, IAH and HOU they are gone and have been.
Any views shared are strictly my own and do not a represent those of any former employer.
 
redcordes
Posts: 244
Joined: Wed Jan 18, 2006 6:28 am

RE: Why Does The Tower Give Out Altimetric Reading

Sat Nov 11, 2006 1:12 am

Quoting IAHFLYR (Reply 11):
OM's are going away very quickly, so I'd use the lightning bolt for an altitude cross check as you won't find any OM's at most U.S. airports for much longer, IAH and HOU they are gone and have been.

Yes, you are absolutely right. The "lightning bolt" is the correct place to look for the GS intercept altitude. Thanks.
"The only source of knowledge is experience." A. Einstein "Science w/o religion is lame. Religion w/o science is blind."
 
N231YE
Posts: 2620
Joined: Tue Jul 25, 2006 9:24 am

RE: Why Does The Tower Give Out Altimetric Reading

Sat Nov 11, 2006 1:23 am

Quoting TheGreatChecko (Reply 6):
Now, because I feel like being picky and this is tech-ops   ...an ATIS (Automatic Terminal Information Service) only exists at a towered airport.

With no tower, its either an ASOS (Automatic Surface Observation System) or AWOS (Automated Weather Observation System) or as I just learned an AWSS (Automated Weather Sensor System).

Yeah, Yeah, ATIS, AWOS, ASOS, blah blah  smile  I figured out that I screwed that up after the "window of opportunity" to edit was closed.
 
Jerald01
Posts: 151
Joined: Sun Oct 08, 2006 11:35 pm

RE: Why Does The Tower Give Out Altimetric Reading

Sat Nov 11, 2006 3:45 am

 airplane  (1) These things are designed to fly from point A to point B. (2) Altimeters readings depend on the pressure of the air around the aircraft to show correct alititude above sea level.

The air pressure at point A at the time of departure may NOT be the same as the air pressure at point B upon arrival. If a pilot sets his altimeter to the field elevation at point A prior to take-off and does NOT re-set it prior to landing at point B the altimeter may not read his actual height above sea level, thereby placing him in danger.
"There may be old pilots, and there may be bold pilots, but there are darn few green cows"
 
pilotpip
Posts: 2820
Joined: Fri Sep 19, 2003 3:26 pm

RE: Why Does The Tower Give Out Altimetric Reading

Sat Nov 11, 2006 4:26 am

Quoting IAHFLYR (Reply 11):
All true but also the ATIS gives runway/s in use, approach to expect, pertinent NOTAMS such as closed taxiway etc., so should something as that change as well then a new ATIS is made..........creepy robotic, information OKER!!

You gotta love ATIS Monster. The first remark the past few years at STL on December 25 has been "Ho Ho Ho". Made even funnier by ATIS Monster.
DMI
 
MrChips
Posts: 933
Joined: Wed Mar 30, 2005 2:56 pm

RE: Why Does The Tower Give Out Altimetric Reading

Sat Nov 11, 2006 6:11 am

Quoting TheGreatChecko (Reply 6):

While the ATIS transmits information, such as weather and runway information, that would congest frequencies at a busier terminal facility and normally do not change more than once an hour. A new one is recorded by the tower each hour unless the weather significantly changes and must be changed. At really large airports, its a creepy robotic voice.

I've always wondered about the use of computer-generated ATIS messages. We have them at large airports here in Canada, and not a word of a lie, the one at YYC takes almost 5 minutes to cycle through.
Time...to un-pimp...ze auto!

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