Originally Posted by
werbil
Pilots can use GNSS for separation, ATC can't. Comparative range and bearing from any waypoint.
Pilots can also use the theoretically impossible to collide self separation standard even though it doesn't comply with an ATC separation standard.
Do you ever consider why ATC can't use these separation standards? Odds are it is because they are not reliable enough.
"theoretically impossible to collide" might be a particularly unreliable standard for aircraft maneuvering in 3 dimensions. I suspect it does actually comply with ATC separation standards, if it can be reliably determined.