Very depressing post that I imagine all of us who fly are reading closely to try to learn from and reduce this very rare tragic occurence.
I was flying yesterday and it was very hazy, as we went over Brize Norton airfield under RIS control going north, a high wing appeared on a direct collision course to us and a very quick manoeuvre was needed. The brize radar had had no contact with the pilot who may be asked on landing to conact them. The point I'm making is not to name & shame but to remind us all that if you are going into airspace, controlled or not where there are ATC's operating for heavens sake talk to them. The more traffic information we all have the better.
(We were in a cirrus where you could see all the transponder active traffic, but this conflicting plane was not squarking charlie, an obvious limitation to TCAS)
Thoughts with all famillies concerned, especially just before Christmas.
LF