When military aircraft "disappear" from the ADS-B & MLAT system, does this mean that all transponders are off? Or do they continue using transponders in a way that only ATC can decode? And which mode is that, Military Mode 5 maybe? Also how does this work in foreign areas, such as where a B-1B training mission is crossing Germany or Poland? I know Russia's military planes for the most part don't appear on ADSBX. Presumably they are visible to Russian ATC, but MLAT cannot be used for some reason? Or do Russian military planes run without transponders?
A recent non-technical BBC news item which I can't find at the moment mentioned that Russian fighter jets were flying near UK airspace with their transponders turned off, thus forming a danger to other airspace users. "This is why the UK scrambled jets from RAF Lossiemouth to intercept". Of course there are other reasons why the UK would intercept Russian fighter jets near UK airspace! Unfortunately I was not "watching" at the time, but I'm not sure I would have seen much anyway... MLAT requires at least 4 (?) ADSBX receivers and unfortunately over the sea N or NE Scotland probably won't get that coverage. In fact I've just looked at the ADSBX MLAT feeder map in that area and not only are there not many feeders, but quite a few of those there are seem to be non-functional at the moment (no sync lines).
