PA-31 Navajo/Chieftan/Mojave/T1040
Air Traffic Control Fully Certified
Other / Unknown
ATC Issue All Types
General None Reported / Taken
ATC Equipment / Nav Facility / Buildings
Pilot visual was being applied throughout the Piper's descent from 6;000 FT. Aircraft were about 2.5 NM apart and the Conflict Alert never activated until the Piper descended through the Caravan's altitude of 5;000 FT and attained standard separation again at 3;900 FT. After separation was lost and then regained; only then did the Conflict Alert activate. The Conflict Alert was definitely not doing its job here and yet we have many instances of two VFR aircraft tail to tail with standard separation and the Conflict Alert is still flashing. Something is amiss. An additional event involved aircraft that crossed paths and Conflict Alert did not activate until aircraft were 2-3 NM apart going away from each other with increasing separation. No Conflict Alert was present while aircraft were 004 apart converging. It should have been activating but did not activate until the event was over. Determine why the Conflict Alert fails to display during a valid conflict situations.
ZSE Controller provided several examples of the Conflict Alert function; which according to the reporter; fails to activate when appropriate.