A C414A PVT PLT HAS AN NMAC WITH AN OVERTAKING BE30 IN CLASS E AIRSPACE NW OF GRN; MEXICO.

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I WAS AT CRUISE IN MY C414A AT 16500 FT FROM LORETO; MEXICO; TO SAN DIEGO BROWN FIELD. I WAS GIVEN A TFC ALERT BY MY SKY WATCH AND SAW ON THE DISPLAY TFC AT 5 O'CLOCK POS; AT +200 FT; ABOUT 2 MI BEHIND. I DISCONNECTED THE AUTOPLT AND BEGAN AN IMMEDIATE DSCNT. I WAS THEN STARTLED TO SEE HOW QUICKLY THE TFC WAS GAINING ON US AND INCREASED PITCH DOWN. I WAS PERPLEXED (AND FRIGHTENED!) TO SEE THE TFC CONTINUING TO APCH VERY CLOSELY AT +200 FT PER THE DISPLAY. WHEN A LAST ATTEMPT TO INCREASE OUR DSCNT RATE FAILED TO INCREASE THE INDICATED +200 FT DIFFERENTIAL; I KEPT MY SAME PITCH DOWN AND VEERED TO THE R. I THE SAW A BE200-300 SERIES KING AIR OUT MY L SIDE WINDOW AND SHORT WAYS BELOW AND AHEAD OF US IN A STEEP DIVE AWAY FROM US TOWARD 10 O'CLOCK POS; FROM OUR ORIGINAL HEADING. WE HAD DSNDED ABOUT 700 FT; THE KING AIR PROBABLY ABOUT 1500 FT. MY PAX HAD SEEN THE KING AIR PASS VERY CLOSELY FROM ABOVE TO THE R BEHIND US TO BELOW AND IN FRONT TO THE L OF US. UPON REFLECTION: 1) WE WERE GPS DIRECT MMLT-KSDM; A LIKELY RTE FOR OTHERS; ALTHOUGH THE KING AIR SEEMED TO BE XING OUR COURSE FROM BEHIND R TO L AHEAD. 2) WE WERE AT 16500 FT CORRECT VFR ALT FOR OUR HEADING -- A LIKELY ALT FOR FASTER PLANES. 3) WHEN THE OTHER PLT SAW US WHILE APCHING FAST FROM BEHIND HE MAY HAVE DECIDED TO PASS BENEATH US; EVEN THOUGH HE WAS INITIALLY ABOVE US SO AS TO BETTER KEEP US IN SIGHT AND WOULD HAVE THEN BEEN SURPRISED WHEN WE BEGAN A RAPID DSCNT TO AVOID HIS APCH. HE SHOULD HAVE DEVIATED UP. PLTS SHOULD BE WARNED TO ALWAYS DEVIATE AWAY FROM OTHER TFC IN ANTICIPATION THAT THE OTHER ACFT MIGHT RESPOND TO A TCASII WARNING AND SUDDENLY ALTER COURSE. IN THIS CASE OUR SKY WATCH WOULD HAVE SAVED US HAD THE OTHER PLT NEVER SEEN US; BUT WHEN THE OTHER PLT DECIDED TO DSND FROM ABOVE TO PASS BELOW US WHILE OVERTAKING US WITH HIS +/-100 KT HIGHER SPD; WE NEARLY COLLIDED WHEN WE DOVE SUDDENLY IN RESPONSE TO THE TFC ALERT.