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  #1  
Old 09-16-2016, 04:42 PM
Bayou Bert's Avatar
Bayou Bert Bayou Bert is offline
 
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Location: Prairieville, LA
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Default APRS Altitude

How accurate is APRS on showing altitude on a flight track?
I have been showing 300 feet higher than what my EFIS says
I flew.
Anyone know?
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  #2  
Old 09-16-2016, 05:16 PM
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Greg Arehart Greg Arehart is offline
 
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Bert,

The reported altitude is GPS altitude from the GPS associated with the APRS radio, which is notoriously inaccurate because of the relatively low angle to the satellites. Could be low or could be high.

Greg
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  #3  
Old 09-16-2016, 05:38 PM
VHS VHS is offline
 
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Location: Napa, CA
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Quote:
Originally Posted by Bayou Bert View Post
How accurate is APRS on showing altitude on a flight track?
I have been showing 300 feet higher than what my EFIS says
I flew.
Anyone know?
The Spec generally calls for 300 feet of CEP. Don't bet your life on it.

Allen
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  #4  
Old 09-16-2016, 05:48 PM
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Brantel Brantel is offline
 
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baro alt and gps alt are two different critters. Much info online about this.
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  #5  
Old 09-16-2016, 06:11 PM
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Steve Melton Steve Melton is offline
 
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I have found GPS altitude to be higher than baro on hot days (above std temp 15C at sea level) and less than baro on cold days. I would bet GPS altitude is more accurate than baro but fly the baro because we all do that. at std temp at sea level and std lapse rate baro and GPS are very close. don't recommend doing this, but if you're in a bind and have to fly an approach using GPS altitude on the a hot day, fly it higher than you would on a cold day.
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Last edited by Steve Melton : 09-16-2016 at 06:23 PM.
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  #6  
Old 09-17-2016, 05:21 AM
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Bayou Bert Bayou Bert is offline
 
Join Date: Sep 2012
Location: Prairieville, LA
Posts: 198
Default Thanks

Thanks to everyone for info. I am getting ready to change out the
static ports on the plane. They were already installed when I bought the
plane at about the 70% complete stage. It has Cessna static ports on
the outside of the skin in the correct location. Far cry from the Vans
pop rivet and IAS, in testing is dubious. Installing Cleveland ports due to
size hole already drilled.
So reason for asking, thanks again for the info.
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