AN EMB120 FO; THE PNF; MAINTAINED EXCELLENT SITUATIONAL AWARENESS AND WAS ABLE TO VECTOR HIS CAPT AROUND A POTENTIAL NMAC ACFT WHEN PSP ATC WAS UNABLE TO HELP.

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DSNDING INTO THE PALM SPRINGS AREA; I WAS THE PNF AND JUST GOT HANDED OFF FROM ZLA TO PSP APCH AT AROUND 15000 FT; MAYBE SLIGHTLY LOWER. ZLA GAVE US A DSCNT INSTRUCTION OF PLT'S DISCRETION TO 11000 FT MSL. WHEN I CHKED IN WITH PSP APCH; I STATED OUT ALT AND DISCRETION TO 11000 FT MSL. THE CTLR RESPONDED IN THE AFFIRMATIVE. AT THIS POINT; I NOTICED ON OUR TCASII A TARGET AT THE 12 O'CLOCK POS AND 10-15 MI OUT. IT WAS SEVERAL THOUSAND FT BELOW US AND CLBING. I HAD VISUAL CONTACT WITH THE TFC AND ASSUMED THAT THE CTLR HAD BEEN HANDLING THIS ACFT ALSO. THIS OTHER TARGET WAS AN ACR MD80 CLBING OUT OF PALM SPRINGS. I ASSUMED HE WAS GOING TO LEVEL SHY OF OUR 11000 FT ALT. THE ACR JET ALSO ASSUMED WE WERE LEVELING ABOVE HIS ALT. WHEN I REALIZED THAT THE OTHER TFC WAS NOT LEVELING AND WE WERE CLOSING QUICKLY ON A COLLISION COURSE; IT WAS (THE OTHER TFC) WITHIN 3 MI. I TOLD THE CAPT IMMEDIATELY TO CHANGE COURSE JUST AS THE CTLR INSTRUCTED US TO TURN IMMEDIATELY TO THE L. THE AIRPLANE WAS STILL ON AUTOPLT AND WAS MAKING A SMOOTH AND SLOW TURN TO THE L WHEN I STATED AGAIN; 'TURN NOW; TURN.' THE CAPT REMOVED AUTOPLT CTL AND BANKED THE ACFT INTO A 50-55 DEG TURN WHILE SLOWING THE DSCNT. AT THIS POINT; I LOST VISUAL CONTACT WITH THE JET DUE TO THE STEEP BANK. WE GOT THE TFC ALERT ON THE TCASII AND AS I WATCHED IT; IT DISPLAYED A -7 SYMBOL; WHICH IS INDICATIVE OF A 700 FT SEPARATION. THE CTLR SAID HE HAD NO IDEA WHAT HAD HAPPENED; BUT WE GAVE HIM OUR LAST ALT AND CALLED HIM FROM THE GND PHONE. IT TURNS OUT THAT THE CTLR CLAIMS THAT THERE WAS A GLITCH IN THE PROBLEMATIC PSP RADAR. IN LIGHT OF THIS INCIDENT; I NOW KEEP A MUCH MORE VIGILANT WATCH OF THE TFC AROUND ME; AND QUERY ATC WHEN I AM UNSURE OF OUR 'TFC.' IN ADDITION; I AM MORE FAMILIAR WITH THE FACT THAT ATC IS NOT PERFECT; BUT TRIES ITS BEST TO SEPARATE TFC.