POTENTIAL CONFLICT AT NON TWR ARPT UNICOM.

Narrative

THIS WAS A LIFEGUARD FLT WITH A DOCTOR. 2 NURSES AND A SICK 3 MONTH OLD BABY ON BOARD. TAXI INFO WAS GIVEN ON UNICOM TO THE EFFECT WE WERE TAXIING TO RWY 14. AN SMA CALLED IN STATING IT WAS NW REQUESTING ARPT ADVISORY. AN ACFT WAS BEING REFUELED AND THIS INDICATED THE UNICOM RADIO IN THE FBO OFFICE WAS PROBABLY NOT MANNED. AFTER WAITING A MIN WITH NO REPLY I ANSWERED THAT THE WIND WAS LIGHT; THAT THE SOCK AT MIDFIELD FAVORED RWY 32 BUT THAT WE WERE TAXIING TO 14 WHERE THE WIND WAS CALM. ON APCHING RWY 14 WE ANNOUNCED OUR INTENTIONS OF DEPARTING 14 WITH A 45 DEG R TURN. THE DOCTOR WAS SITTING IN THE COPLT SEAT AND HAD ASSISTED IN SPOTTING OTHER ACFT ON THE INBOUND LEG. CLBING OUT SOMEWHERE BTWN 1500 AND 1800 FT WITH LNDG LIGHTS EXTENDED THE SMA SUDDENLY APPEARED FROM BEHIND THE WINDSHIELD CTRPOST MOVING R TO L. ESTIMATED DISTANCE WAS 1/4 MI AND 400-500 FT ABOVE. MY INITIAL REACTION WAS TO DIVE WHICH CAUSED THE NURSES IN THE REAR SOME DISCOMFORT. THE DOCTOR STATED HE HAD ASSUMED I HAD HAD THE ACFT IN SIGHT ALL ALONG. I ASKED THE SMA PLT IF HE HAD SEEN THE TWIN GO BY AND HE ANSWERED 'YES.' HIS CASUALNESS INDICATED HE HAD NOT CONSIDERED US A COLLISION THREAT. MY CTL INPUT WAS THE RESULT OF SUDDENLY SEEING THE OTHER ACFT AT AN UNCOMFORTABLY CLOSE RANGE. I HAVE ALWAYS RPTED SEEING OTHER ACFT WHILE STILL ON UNICOM IN THE ARPT VICINITY BUT OBVIOUSLY THE SMA PLT DID NOT FEEL THIS WAS NECESSARY. THE DOCTOR WILL BE A BETTER FRONT SEAT PAX.