A B757 CARGO CAPT RPTED THAT; DURING AN OUTAGE AT ZLA; HE FOLLOWED A TCASII RA TO AVOID A C750.

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WE WERE IN CRUISE FLT FL350. AFTER SWITCHING FROM ZAB TO ZLA; THERE WAS A PAUSE IN CONVERSATION OF APPROX 10 MINS. ZLA HAD A MAJOR DISRUPTION IN THEIR ABILITY TO COMMUNICATE. WHEN WE REALIZED THIS; WE ATTEMPTED SEVERAL OTHER ZLA FREQS AND THEN TRIED TO RAISE SOCAL APCH CTL. DURING THIS TIME AT 20-40 MI DUE E OF PSP VOR; ANOTHER ACFT FLEW WITHIN THE BOUNDARY OF OUR TCASII. TCASII COMMANDED CLB XING CLB. WE IMMEDIATELY COMPLIED AND CLBED TO FL360 AT WHICH TIME TCASII SIGNALED CLR OF CONFLICT. WE WERE ABLE TO ESTABLISH CONTACT WITH SOCAL APCH SHORTLY AFTER LEVEL OFF AT FL360 AT WHICH TIME THEY TOOK OVER CTLR DUTIES FOR ZLA. WE MADE A NORMAL APCH AND LNDG INTO SANTA ANA; CA. TCASII IS A LIFE SAFER! SUPPLEMENTAL INFO FROM ACN 631166: I WAS ACTING AS PIC OF A CITATION X UNDER THE RULES OF FAR PART 91 ON A TRIP FROM PHOENIX; AZ; TO MONTEREY; CA; WHEN AN UNPRECEDENTED EVENT OCCURRED. ZLA HAD A TOTAL LOSS OF PRIMARY AND SECONDARY MEANS OF 2-WAY RADIO COM. AFTER NUMEROUS FUTILE ATTEMPTS TO REGAIN RADIO CONTACT WITH ZLA; IT BECAME EVIDENT THAT THERE WAS A SERIOUS COMS PROB ON THEIR PART. WE IMMEDIATELY BEGAN TO MONITOR THE EMER FREQ (121.50). THIS EVENT OCCURRED SHORTLY AFTER WE REACHED OUR CRUISING ALT OF FL350 AND HAD BEEN ISSUED A CLRNC DIRECT TO PMD J6 AVE DIRECT MRY. THE PREVAILING CONDITIONS WERE VMC AND THE VISIBILITY WAS UNRESTR WHICH HAD NO ADVERSE EFFECT ON THIS EVENT. AS LOSS OF RADIO COMS PROCS DICTATE; WE WERE CONTINUING TO OUR CLRNC LIMIT WITH FULL EXPECTATION OF REGAINING RADIO COM WITH ZOA UPON XING THEIR AIRSPACE BOUNDARY. ON OUR RTE OF FLT; ZOA AIRSPACE BEGAN AT A POINT JUST N OF THE AVE VOR; AS DEPICTED ON THE HIGH ALT ENRTE CHART. AFTER A FEW MINS HAD ELAPSED; WE NOTICED A TCASII TARGET HAD APPEARED AT OUR ALT AND AT OUR 2 O'CLOCK POS AT A RANGE OF APPROX 15 MI. WE QUICKLY MADE VISUAL CONTACT WITH THE TARGET AND VERIFIED THAT WE WERE INDEED ON A SLOWLY CONVERGING COURSE WITH AN ACR B757. NOT BEING ABLE TO COMMUNICATE WITH ATC; WE WERE FORCED TO WAIT FOR A TCASII RA BEFORE CHANGING ALT. WE SUBSEQUENTLY RECEIVED THE RA TO WHICH WE RESPONDED ACCORDINGLY AND BROADCASTED OUR ACTIONS ON THE EMER FREQ AS WELL AS OUR LAST ASSIGNED ZLA FREQ. DURING THE MANEUVER; WE TEMPORARILY REGAINED 2-WAY RADIO COMS WITH ZLA AND WERE ISSUED A NEW ALT CLRNC OF FL310. SHORTLY THEREAFTER; COMS WITH ZLA WERE ONCE AGAIN LOST. AS THE FLT CONTINUED; WE WERE TOLD BY AN UNIDENTED CTLR ON THE EMER FREQ TO CONTACT JOSHUA APCH; WHICH WE DID. WE REMAINED IN CONTACT WITH JOSHUA APCH UNTIL WE REACHED THE ZOA BOUNDARY WHERE THE FLT CONTINUED TO MONTEREY WITHOUT FURTHER INCIDENT. HAD THIS EVENT OCCURRED UNDER IMC AND WITHOUT THE IMPLEMENTATION OF TCASII TECHNOLOGY; I AM CERTAIN THE OUTCOME WOULD HAVE BEEN TRAGIC. FORTUNATELY; THE TCASII ABOARD THE ACFT DID ITS JOB PERFECTLY AND; AT NO TIME WAS SAFETY OF FLT COMPROMISED. AT THE TIME OF THE INCIDENT; I DID NOT KNOW WHAT COULD HAVE BEEN DONE TO PREVENT A RECURRENCE OR TO CORRECT THE SIT WITHOUT KNOWING THE CAUSE. I LATER LEARNED THAT THE PROB WAS ATTRIBUTED TO HUMAN ERROR. ACCORDING TO THE NEWSPAPERS; THE FAILURE ON THE PART OF A TECHNICIAN TO PERFORM REQUIRED ROUTINE MAINT WAS THE CAUSE OF THE FAILURE OF THE PRIMARY COMS SYS. SUBSEQUENTLY; THE SECONDARY SYS ALSO FAILED AS A RESULT OF AN ADDITIONAL TECHNICIAN ERROR ACCORDING TO OFFICIALS. IN LIGHT OF THESE EVENTS; I FEEL CERTAIN THAT THE APPROPRIATE OFFICIALS ARE TAKING THE NECESSARY STEPS TO PREVENT A RECURRENCE OF THIS BIZARRE EVENT.