EVASIVE ACTION BY BOTH ACFT TO PREVENT MIDAIR COLLISION.

Narrative

THE F/O WAS FLYING THE ACFT ON DSCNT INTO MFR. AS PNF; I WAS WORKING THE RADIOS. THE WX WAS CAVU AND THE AIR SMOOTH. MFR HAS APCH CTL BUT IS NON RADAR. WE HAD BEEN CLRED FOR A VISUAL APCH WHEN MFR APCH INFORMED US THAT SMT Y WOULD BE DEPARTING VFR NBND. WE WERE SBND FROM THE N INTO MFR. AFTER A SHORT TIME; I INQUIRED MFR APCH AS TO THE POS OF THE TFC. MFR APCH SAID THAT HE (THE TFC) SHOULD BE UP ON FREQ NOW. MFR APCH THEN ASKED SMT Y HIS POS. SMT Y SAID HE WAS ABEAM THE VOR AT 4000'. AT THAT INSTANT WE WERE DSNDING THROUGH 4800' AT A SPD OF 230 KTS. WE IMMEDIATELY LEVELED OFF AT APPROX 4600'. ALSO AT THIS INSTANT WE WERE AT 3 DME E OF THE VOR; THE SAME POS SMT Y HAD RPTED. MFR APCH THEN REPEATED SMT Y'S POS; WHICH WAS STEPPED ON BY SMT Y. I RESPONDED 'STEPPED ON.' MFR APCH THEN REPEATED THE RPT. I FIRST SAW SMT Y AT 12 O'CLOCK; SAME ALT; AT A DISTANCE OF APPROX 1000'. I IMMEDIATELY REACHED UP AND INITIATED THE ACFT INTO A RIGHT TURN. AT THE SAME TIME I SAID TO MY F/O; 'RIGHT TURN; NOW!' THE TWIN; A LIME GREEN SMT; PASSED BY OUR LEFT SIDE AT THE SAME ALT AT A HORIZ DISTANCE OF APPROX 400-600'. SMT Y APPARENTLY DID NOT SEE US UNTIL HE WAS RIGHT NEXT TO US; FOR HE MADE NO EVASIVE ACTION UNTIL THAT POINT; WHEN HE ALSO BANKED HARD RIGHT. I THEN INFORMED MFR APCH THAT WE HAD TAKEN EVASIVE ACTION TO AVOID SMT Y. HAD NO ACTION BEEN TAKEN; A COLLISION WOULD HAVE RESULTED. SEVERAL FACTORS CONTRIBUTED HERE. THE FRONTAL VIEW OF A SMT IS VERY THIN AND HARD TO SEE. SMT Y WAS ALSO NOT SHOWING ANY LNDG; RECOGNITION OR STROBE LIGHTS. THIS PARTICULAR SMT Y WAS LIME GREEN AND BLENDED IN VERY WELL WITH THE SURROUNDING TERRAIN. MEDFORD; OR; SITS IN A DEEP VALLEY WITH A LOT OF AIR TFC; ESPECIALLY N AND S. THE MOST IMPORTANT FACTOR HERE IS THAT MFR HAS NO RADAR! RADAR IS SCHEDULED TO BE INSTALLED IN 1991. LET'S CONTINUE TO HOPE THAT MANUAL APCH CTL AND THAT SEE AND AVOID PREVENTS AN ACCIDENT UNTIL 1991! LET'S USE SOME OF THE TRUST FUND MONEY TO HELP FIX THESE PROBS!