Avidyne Homepage
Forum Home Forum Home > Avidyne General > AXP340/322 ADS-B Transponder
  New Posts New Posts RSS Feed - Why does my AXP 322 transponder show 300' low?
  FAQ FAQ  Forum Search   Register Register  Login Login

Why does my AXP 322 transponder show 300' low?
 Post Reply Post Reply
Author
Message
  Topic Search Topic Search  Topic Options Topic Options
warrenc View Drop Down
Newbie
Newbie
Avatar

Joined: 27 May 2015
Location: Tampa Bay
Status: Offline
Points: 11 		Post Options Post Options   Thanks (0) Thanks(0)   Quote warrenc Quote  Post ReplyReply Direct Link To This Post Topic: Why does my AXP 322 transponder show 300' low?
    Posted: 28 Mar 2016 at 9:08pm
I have noticed that my AXP322 transponder shows 300' low when ADSB out is interegated, but right on altitude when with center/approach.  The following flight from Tallahassee to Sarasota is an example.  Cruising at 9,000', ADSB shows 8,700' the whole way, except for one hit from Jacksonville, about half way down, has me at 9,000'.  Sorry the following tracklog isn't a URL.  Is this just an adjustment somewhere?  (Fighting a 20K headwind)

http://flightaware.com/live/flight/N777YM/history/20160308/1400Z/KTLH/KSRQ/tracklog
Warren
Back to Top
pburger View Drop Down
Senior Member
Senior Member
Avatar

Joined: 26 Dec 2013
Location: United States
Status: Offline
Points: 406 		Post Options Post Options   Thanks (0) Thanks(0)   Quote pburger Quote  Post ReplyReply Direct Link To This Post Posted: 29 Mar 2016 at 9:30am
Your transponder is reports and shows the "pressure altitude" from your encoder.  The encoder altitude is based on a 29.92 altimeter setting.  The only time your pressure altitude will match your actual altitude is when the altimeter setting is 29.92.

What was your altimeter setting at the time?

I assume that "Flightaware ADSB" sources don't correct for the local altimeter settings along the route. (It looks like they just pass the pressure altitude as received from the ADSB data packet.)  ATC facilities (like a Center or Approach facility) do correct for the local altimeter setting, and should match what you see on your altimeter.




Edited by pburger - 29 Mar 2016 at 9:40am
Back to Top
AviSimpson View Drop Down
Senior Member
Senior Member


Joined: 31 Mar 2015
Location: Lincoln, MA
Status: Offline
Points: 765 		Post Options Post Options   Thanks (0) Thanks(0)   Quote AviSimpson Quote  Post ReplyReply Direct Link To This Post Posted: 29 Mar 2016 at 9:34am
Originally posted by warrenc warrenc wrote:

I have noticed that my AXP322 transponder shows 300' low when ADSB out is interegated, but right on altitude when with center/approach.  The following flight from Tallahassee to Sarasota is an example.  Cruising at 9,000', ADSB shows 8,700' the whole way, except for one hit from Jacksonville, about half way down, has me at 9,000'.  Sorry the following tracklog isn't a URL.  Is this just an adjustment somewhere?  (Fighting a 20K headwind)

http://flightaware.com/live/flight/N777YM/history/20160308/1400Z/KTLH/KSRQ/tracklog

PM sent
Simpson Bennett
Avidyne Corporation
Product Manager
Back to Top
 Post Reply Post Reply
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.01
Copyright ©2001-2018 Web Wiz Ltd.

This page was generated in 0.106 seconds.