SMA ACFT INSTRUCTOR AND TRAINEE LOST COM WITH DEP CTLR IN SJC CLASS C AIRSPACE AND AS A RESULT; A LESS THAN LEGAL SEPARATION LTSS OCCURRED WITH AN ACR ACFT.

Narrative

MY STUDENT AND I DEPARTED SJC ON A VFR CLASS C CLRNC. PROCEEDING SE; WE WERE GIVEN A HDG TO KEEP US TO THE R OF THE INBOUND FINAL APCH COURSE FOR INBOUND AIRLINE TFC. APPROX 5 MI OUT; WE WERE TOLD BY BAY DEP TO 'RESUME OWN NAV.' APPROX 15 MI OUT; WE SAW HEAD-ON AIRLINE TFC APCHING HEAD-ON; AND BOTH OF US HAD TO TAKE EVASIVE ACTION. AFTER WE HAD PASSED; I REALIZED THAT OUR SELECTED COM RADIO HAD SOMEHOW BEEN SWITCHED OFF OF BAY DEP; WHICH EXPLAINED WHY WE HAD NOT GOTTEN TA'S. WE RE-ESTABLISHED CONTACT; AND BAY DEP CONFIRMED THAT THEY HAD BEEN TRYING TO REACH US. IRONICALLY; I WAS EXPLAINING TO MY STUDENT THAT WE NEEDED TO STAY ON DEP FREQ UNTIL THEY ASSIGNED A NEW ONE OR ADVISED US THAT FREQ CHANGE WAS APPROVED. AT THAT POINT; ONE OF US INADVERTENTLY 'FLIPPED THE SWITCH.' THE MAIN FACTORS WERE: INADEQUATE PREFLT BRIEFING AND PREPARATION OF THE STUDENT BY THE INSTRUCTOR ON CLASS C ATC PROCS IN CONGESTED AIRSPACE; TRYING TO EXPLAIN TOO MUCH DURING A PERIOD OF HIGH WORKLOAD; AND DISTRS. ONE OF THE ITEMS I WAS TRYING TO EXPLAIN WAS A PROC FOR USING #2 COM TO MONITOR TFC AT OUR NEXT DEST; AN UNCTLED ARPT 30 MI SE OF SJC. THIS ENDED UP CONTRIBUTING TO THE CONFUSION; SINCE IT APPEARS THAT MY STUDENT FLIPPED THE #1 COM SWITCH INSTEAD OF TUNING THE CTAF IN #2 COM. IN RETROSPECT; I BELIEVE IT WOULD HAVE BEEN BETTER TO LET THIS WAIT UNTIL WE WERE WELL OUT OF SJC AIRSPACE; EVEN IF IT MEANT CIRCLING OVER OUR DEST WHILE WE GOT ASOS AND TA'S.