Why does my AXP 322 transponder show 300' low?
Printed From: Avidyne
Category: Avidyne General
Forum Name: AXP340/322 ADS-B Transponder
Forum Description: Topics on the Avidyne AXP340/322 ADS-B Transponder
URL: https://avidynelive.com/forum_posts.asp?TID=1019
Printed Date: 26 Mar 2026 at 3:17pm
Software Version: Web Wiz Forums 12.07 - https://www.webwizforums.com
Topic: Why does my AXP 322 transponder show 300' low?
Posted By: warrenc
Subject: Why does my AXP 322 transponder show 300' low?
Date Posted: 28 Mar 2016 at 4:08pm
|
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 |
Replies:
Posted By: pburger
Date Posted: 29 Mar 2016 at 4:30am
|
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. |
Posted By: AviSimpson
Date Posted: 29 Mar 2016 at 4:34am
PM sent ------------- Simpson Bennett Avidyne Corporation Product Manager |
warrenc wrote: