shagpile
Sure I'm flying 500' visual but what if the GPS logged me as 400ft.
Serious question for all from a retired avionics tech... and please don't slag me off for this; I have been retired now for 5 years and things may have changed...!
I was under the impression that ADS-B altitude information is derived from a precision barometric altimeter as in the case of TCAS and RVSM ops. The reason being that altitude information from a GPS derived source is not considered sufficiently accurate. Using your example a situation exists whereby a pilot could in fact have three or four different altitude indications displayed in the cockpit... barometric as when set to QFE, barometric as when set to QNH, GPS alt and Radio Altimeter... not forgetting altitudes when flying above transition levels when QFE and QNH are irrelevant. I appreciate that the latter case does not come into the equation at 500' but which 500' are we to depend upon...
Anyone?