C152 AND BE55 HAVE CLOSE ENCOUNTER ON APCH TO STS. STUDENT PLT OF C152 UTILIZING UNICOM FREQ VICE CTAF TO PROVIDE TA'S.

Narrative

THE PROB AROSE WHEN MY STUDENT WAS FLYING SOLO IN VMC DAYLIGHT/DUSK AFTER TWR HAD CLOSED. THE STUDENT HAS EXTENSIVE PRE-SOLO EXPERIENCE OPERATING OUT OF BOTH CTLED AND UNCTLED FIELDS. HE HAD BEEN INSTRUCTED TO MAKE FULL STOP LNDGS AT SANTA ROSA; WITH PATTERNS TO THE L; AND TO RPT HIS POS ON CTAF AFTER TWR CLOSED. HE COMPLIED WITHOUT APPARENT INCIDENT; EXCEPT THAT WHILE WE WERE DEBRIEFING THE FLT; AN IRATE BARON DRIVER STORMED IN STATING THAT HE ALMOST OVERRAN A C152 ON FINAL AND ASSERTED THAT THE CESSNA WAS NOT MAKING RADIO CALLS. THE STUDENT; WHO IS NORMALLY VERY GOOD; ALBEIT SOMEWHAT AWKWARD ABOUT MAKING RADIO CALLS; ASSERTED THAT HE HAD INDEED MADE CALLS THAT HE SAW (BUT DID NOT HEAR) THE BARON; COUNTED HIM NO FACTOR (ON APPROX 4 MI FINAL) AND WAS UNAWARE OF THE CONFLICT. UPON FURTHER EXAMINATION IT BECAME APPARENT THAT MY STUDENT HAD USED UNICOM FREQ TO MAKE HIS RPTS INSTEAD OF CTAF. THE UNICOM/CTAF FREQS ARE THE SAME FREQ AT ALL OF THE OTHER UNCTLED FIELDS WE HAD USED; AND HE ASSUMED THAT THIS WOULD BE THE CASE AT SANTA ROSA. HIS INTERP OF HIS POS RELATIVE TO THE BARON WAS BASED UPON EXPERIENCE WITH ACFT OF LIKE TYPE IN CTLED AIRSPACE OF SANTA ROSA; AND WITH LIGHT PISTON SINGLES AND TWINS AT THE SURROUNDING NON-CTLED FIELDS. HE WAS NOT AWARE OF; OR ELSE DID NOT TAKE INTO ACCOUNT; THE DIFFERENCE IN APCH SPDS BTWN A BARON AND A C152; AND DISCOUNTED A COLLISION THREAT AS A NON HAZARD.