Indeed, but all the emitters with “dodgy” baro altitude will be 0 or 1
SIL does not involve Baro Altitude or Geo Altitude, it is the Source Integrity Level or IOW the trustworthiness of the position source. A SIL of 3 indicates that the probability of exceeding the horizontal NIC containment radius is less than or equal to 1 X 10 exp -7.
Only in that SIL=3 is an indicator that the other aircraft has a reasonably accurate baro altitude.
Otherwise, how could one tell?
Peter wrote:
If Yes then I am surprised that the receivers such as the Skyecho 2 don’t automatically select the GPS value and discard the baro value, if the GPS value is available and especially if the received signal is SIL=3 which is telling it that there is likely to be a significant baro altitude mismatch.
I don’t understand the relevance of SIL.
Not so sure. The TB20 is no speed machine; lots of people will be looking at putting one of these portable gadgets into an RV etc etc.
Would a GTX335 or similar certified ADS-B OUT device be radiating both baro and GPS altitude?
If Yes then I am surprised that the receivers such as the Skyecho 2 don’t automatically select the GPS value and discard the baro value, if the GPS value is available and especially if the received signal is SIL=3 which is telling it that there is likely to be a significant baro altitude mismatch.
Yes, but you fly the kind of plane that tends to have fancier avionics.
I see a 100ft delta at low level and some 200ft higher up, say FL120.
Reading the SkyEcho 2 website information, it includes a baro altimeter that would sense cabin pressure altitude. If connected to ForeFlight, the ownship data provided by the SkyEcho 2 would be used and it includes the pressure altitude sensed from the cabin. So depending on the error between cabin altitude and actual pressure altitude, one would need to compensate for any difference. If you set the ships altimeter to standard 29.92 inches or 1013 MB, a pilot can compare the two in flight to gage how much error is added.
Peter wrote:
How does that work in a cockpit, where the pressure is typically a few mb less than outside
In my experience, the difference has been under 50 feet (1.5mb). “A few” mb difference would probably indicate an aircraft of sufficient performance that it will have rather fancier avionics than needing a portable ADS-B transmitter.
Exactly, so what would e.g. a SkyEcho 2 show in relative altitude, when displaying an ADS-B target whose baro altitude is “transponder accuracy”?
