Accuracy of Transmitted ADS-B Data

#1
A few minutes ago an EasyJet flight into Londond Southend (EZY7416) passed overhead and I clicked onto my PF map view.
I used to lose flights into SEN at about 250', but of late have been able to follow them down to the runway and even see them make the turn at the end onto the taxiway.
Today, the quoted altitude on touchdown was -200' and, as there was no bang and pall of smoke, this must be wrong;). The same happened with the following flight (EZY7436). The alt. details on planefinder.net were the same (I suppose if it is only recording my input it would be, but I'm sure others in the area are providing).

Is this due to incorrect altimeter settings on the aircraft with air pressure differences between take-off locations and landing? I know from using a scanner that SEN always gives incoming a/c local pressure.

SEN is 5 mls away and quoted at 17m elevation and my antenna is about 13m asl, with a low (40m) rise between SEN and me.

Any ideas?
 
#2
I think all the ADSB reported altitudes are referenced to a pressure of 1013. Therefore if the local QFE is say, 1030 all the aircraft will appear to burrow into the runway. Alternatively, if the QFE is 990 they will taxi around several hundred feet over the runway! I live just 1.2 km from GLO (EGBJ) and see this all the time.

Martin
 

Lee Armstrong

Administrator
Staff member
#3
I think all the ADSB reported altitudes are referenced to a pressure of 1013. Therefore if the local QFE is say, 1030 all the aircraft will appear to burrow into the runway. Alternatively, if the QFE is 990 they will taxi around several hundred feet over the runway! I live just 1.2 km from GLO (EGBJ) and see this all the time.

Martin
Yes this is correct :-D