Originally Posted by
Clinton McKenzie
Thanks swh.
What determines whether an ADS B data packet transmitted by an aircraft ‘chooses’ the encoded pressure altitude rather than the GNS height above the WGS-84 geoid? And if the encoded pressure altitude is transmitted in the ADS B data packet, what ‘chooses’ and how is the 25’ versus 100’ resolution ‘chosen’?
The default is encoded pressure altitude, if the encoded pressure altitude is not available GNSS height will be transmitted. Similar with speed the default is GNSS ground speed, and track is computed from the resolving the easting and northing ground speed. In the absence of GNSS ground speed it will transmit IAS and heading if this data is available.
Per the standard, for altitudes below 50187.5 ft it is in 25 ft increments, above that it is 100 ft.