Slightly OT but perhaps relevant to the ADS-B discussion but do they (sometimes) turn the transponders off when over the fireground?
Reason for the question/observation was that in early 2019 we had a fire nearby and I watched the 737 and RJ85 come down and work the fires. Now I regularly see aircraft on FR24 and the like at about 6000' but the 737 and lead aircraft came down and the lead was visible at say 10000' but the 737 droped off at 15000'.
In December 2019 we had another fire nearby and the C130 and RJ85 were usually "visible" at about 6000' and above but not below that which is probably topography.
Most of the military aircraft involved in the bushfire recovery don't appear on FR24 but do on the global adsb exchange.