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Old 13th Mar 2019, 08:21
  #959 (permalink)  
DaveReidUK
 
Join Date: Jan 2008
Location: Reading, UK
Posts: 11,265
Originally Posted by El Bunto View Post
Also the altitude reported in ADS-B depends on the message type being parsed; some use the barometric pressure from the Mode-C source to calculate altitude per 1013hPa*, whereas others use the GNSS height corrected to WGS84. There's no AMSL data from ADS-B.
Yes, although AFAIK the altitudes on FR24 always come from Airborne Position messages, which in turn always contain baro alt.

And of course if you know the QNH and altitude, as we do in this case, it's straightforward to apply the appropriate pressure correction to work out AMSL.
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