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Author Topic: Importance of Proper Altimeter Setting  (Read 15252 times)
bcrosby
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« on: January 21, 2008, 03:30:11 PM »

Some background.

YKZ is inside YYZ (Toronto International) class C rings. As such, altitude in the YKZ zone is restricted to 2500', as (depending on the winds) arrivals to YYZ will be overflying the zone at 3000'

This was the case today and a pilot seems to have either the wrong altimeter setting or is confused as to where he is.

(I'm assuming from his foreign callsign, he's not too familiar with the airspace).

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RayZor
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« Reply #1 on: January 21, 2008, 09:51:39 PM »

ouch, this is another clip that is almost painful to listen to.  (reminds me of the clip in which the pilot COULD NOT understand the controller, despite at least 5 readbacks of the frequency).  This is a textbook example of why to keep your altimeter set accurately, especially if you are skirting just above or below major sections of airspace.
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njf520
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« Reply #2 on: January 22, 2008, 02:04:03 PM »

warning: newbie question...
hi, folks.  just started reading this site a couple weeks ago.

can some explain why the tower reads the altimeter to approaching pilots?
my guess is that the pilot inputs the barometric pressure given by the
tower into their on-board altimeter so it calibrates it.  does that then
give them the distance to the ground at the airport or the distance to
sea level?  thanks...
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KSYR-pjr
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« Reply #3 on: January 22, 2008, 02:33:02 PM »

hi, folks.  just started reading this site a couple weeks ago.

Welcome.

can some explain why the tower reads the altimeter to approaching pilots?
my guess is that the pilot inputs the barometric pressure given by the
tower into their on-board altimeter so it calibrates it.  does that then
give them the distance to the ground at the airport or the distance to
sea level?  thanks...

Speaking for US aviation all charted obstacle elevations (both man-made and natural), airport elevations, and runway touchdown zones are given relative to sea level.     Aircraft are given altitudes to fly (if being controlled by ATC) relative to sea level if below 18,000 feet - at 18,000 feet and above aircraft are given flight levels, which are altitudes based on a standard barometric pressure of 29.92 inches. 

Tower (and all airborne ATC positions) provides an altimeter setting/barometric pressure reading so that, yes, the pilot will enter the setting into the aircraft's altimeter or double check the setting that was provided by a previous controller.  This ensures that a) the pilot knows where the ground and obstacles are in relation to the aircraft, as well as the elevation of the runway touchdown zone and b) ATC will have a common setting for all aircraft within his/her control area.   Again, an aircraft altimeter is set relative to sea level, not ground level since there really could be no standard set to such a varying surface. 

I have read that aerobatic aircraft do set their altimeters relative to ground level when they are performing, but not being an aerobatic pilot I could not confirm this.


edit:  Added note about flight levels
« Last Edit: January 22, 2008, 02:40:18 PM by KSYR-pjr » Logged

Regards, Peter
ATC Feed:  Syracuse (KSYR), NY
bcrosby
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« Reply #4 on: January 22, 2008, 03:23:50 PM »

I just want to clarify one thing.

Altimeter setting and barometric pressure are two separate things.

The altimeter setting is the barometric pressure adjusted for the station/airport height above sea level.

The barometric pressure is the pressure of the atmosphere at sea level.

(For those of you that can decode METARs) You will notice that in Canadian METARs, the sea level pressure (current barometric pressure) is given in the remarks section:

METAR CYKZ 222000Z 24010KT 2 1/4SM -SN BKN011 BKN016 OVC021 M01/M03
A2972 RMK SC5SC2SC2 SLP074=

This indicates that the sea level pressure (SLP) is 1007.4 hPa
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njf520
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« Reply #5 on: January 22, 2008, 09:44:15 PM »

hi, folks.  just started reading this site a couple weeks ago.

Welcome.

can some explain why the tower reads the altimeter to approaching pilots?
my guess is that the pilot inputs the barometric pressure given by the
tower into their on-board altimeter so it calibrates it.  does that then
give them the distance to the ground at the airport or the distance to
sea level?  thanks...

Speaking for US aviation all charted obstacle elevations (both man-made and natural), airport elevations, and runway touchdown zones are given relative to sea level.     Aircraft are given altitudes to fly (if being controlled by ATC) relative to sea level if below 18,000 feet - at 18,000 feet and above aircraft are given flight levels, which are altitudes based on a standard barometric pressure of 29.92 inches. 

Tower (and all airborne ATC positions) provides an altimeter setting/barometric pressure reading so that, yes, the pilot will enter the setting into the aircraft's altimeter or double check the setting that was provided by a previous controller.  This ensures that a) the pilot knows where the ground and obstacles are in relation to the aircraft, as well as the elevation of the runway touchdown zone and b) ATC will have a common setting for all aircraft within his/her control area.   Again, an aircraft altimeter is set relative to sea level, not ground level since there really could be no standard set to such a varying surface. 

I have read that aerobatic aircraft do set their altimeters relative to ground level when they are performing, but not being an aerobatic pilot I could not confirm this.


edit:  Added note about flight levels

thanks very much.  this helps a lot.

one follow-up:

so, if i listen to the JFK tower for a week, will the altimeter always be the same?  or does it change as pressure changes?   thanks again.
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Jason
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« Reply #6 on: January 22, 2008, 09:54:52 PM »

so, if i listen to the JFK tower for a week, will the altimeter always be the same?  or does it change as pressure changes?   thanks again.

The local altimeter setting changes depending on the barometric pressure, so it changes often.  Altimeter settings are transmitted via ATIS broadcasts, ATC transmissions, METARs, and by pilot request (from ATC, FSS, etc).
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Hollis
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« Reply #7 on: January 22, 2008, 11:01:09 PM »

The international standard atmosphere (ISA) is defined as at a mean sea level reference point (MSL), atmospheric pressure is 29.92 inches of mercury (about 1012 millibars in the Metric system), and OAT at 59F or 15C.
During adverse weather, the pressure will be lower. Conversely, on a fine sunny day it will be higher.
Actual clearance above ground (AGL) can only be determined by a radar altimeter (or in VFR conditions, by your eyeballs!).
(If you want the altimeter setting at some remote airport, set the altimeter to the field elevation, which is usually painted on the hangar).
And yes, for many airshow and certain flight test purposes, the altimeter is set to zero altitude prior to take-off.


 
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aviator_06
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« Reply #8 on: January 24, 2008, 08:22:57 PM »

The FAA should make it mandatory to pass a speaking test of some sort because of pilots like this. Well this pilot you could understand a little, but there have been pilots on the CTAF freqs. when im flying that all i hear is "ALALALALA" and sometimes if your lucky you can make out "esessna" or something like that. One of these pilots will cause an accident one day and something needs to be done before that happens. Any one else Agree?
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KSYR-pjr
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« Reply #9 on: January 24, 2008, 08:37:02 PM »

Any one else Agree?

No, because as of now aircraft without radios still fly in the US airspace.  Until (if ever) these aircraft stop flying, other pilots have to remember that the radio is not the only means of avoiding a paint trading session. 
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Regards, Peter
ATC Feed:  Syracuse (KSYR), NY
penguin44
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« Reply #10 on: January 25, 2008, 03:40:15 PM »

This happens far to often at YKZ with people who don't understand the language and/or don't read their charts. I have seen some of the big boys get moved around because of it.
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aviator_06
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« Reply #11 on: January 26, 2008, 06:49:28 PM »

Any one else Agree?

No, because as of now aircraft without radios still fly in the US airspace.  Until (if ever) these aircraft stop flying, other pilots have to remember that the radio is not the only means of avoiding a paint trading session. 

I'm talking about the people talking on the CTAF/ATC Freqs. not the aircraft.
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KSYR-pjr
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« Reply #12 on: January 26, 2008, 07:23:16 PM »

I'm talking about the people talking on the CTAF/ATC Freqs. not the aircraft.

Ever flown to an airport that has a very common CTAF, one that is shared by two or three other nearby airports?   What happens on a sunny, summer Saturday morning on 122.8 at this airport?  Nothing but heterodynes.   Getting a good SA picture from the radio is pretty much useless.  Yet, there are not a lot of accidents caused by this issue.

How is that scenario different than one person who cannot speak well on the CTAF (let's put aside the scenario of this person on an ATC frequency for this one moment)?   

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Regards, Peter
ATC Feed:  Syracuse (KSYR), NY
klhr
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« Reply #13 on: January 26, 2008, 07:48:57 PM »

Has anyone picked up a similar issues from today in Toronto for a C-FJES? I had heard soemtime around 1430-1530L that it was flying up around 5000ft, right in the path of Toronto International, but talking to a totally differeint airport
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Yegger
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« Reply #14 on: January 27, 2008, 01:23:03 AM »

Has anyone picked up a similar issues from today in Toronto for a C-FJES? I had heard soemtime around 1430-1530L that it was flying up around 5000ft, right in the path of Toronto International, but talking to a totally differeint airport
A different airport? Downsview?
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