CLOSE PROX ACR-MLG GA-SMA N OF RSW.

Narrative

WHILE DEPARTING THE FT MYERS ARPT (RSW) WE WERE ON A VECTOR HDG 360 DEG CLBING THROUGH APPROX 9700 FT FOR 10000 FT ASSIGNED WHEN THE CAPT YELLED 'TFC.' I WAS FLYING AND HAD BEEN LOOKING STRAIGHT AHEAD. SKIES WERE MOSTLY CLR WITH A FEW SCATTERED CUMULUS CLOUDS. I LOOKED L AND SAW A BLUE AND WHITE SMA PASS OVER THE TOP OF THE COCKPIT AT 50-100 FT. MY FIRST THOUGHT WAS THAT HE WOULD HIT OUR TAIL. HE WAS WBOUND AND DID NOT APPEAR TO HAVE SEEN US. OUR TCASII WAS ON AND GAVE NO INDICATION OF TFC. DEP CTL SAID THEY SAW NO TFC IN OUR VICINITY. APPARENTLY OUR TFC WAS AT 10000; VFR WITHOUT A TRANSPONDER. I WAS THINKING ABOUT LIGHT ACFT TFC; SINCE WE WERE BEING HELD DOWN LOW FOR A CONSIDERABLE TIME. MY ATTN WAS DIVIDED BTWN TCASII; LOOKING OUTSIDE AND MONITORING THE LEVEL OFF. I DON'T KNOW WHY WE DIDN'T SEE THE TFC. POSSIBLY HIS POS WAS HIGH ENOUGH TO BE BLOCKED BY THE WIND SCREEN. HE PROBABLY DID NOT SEE US DUE TO HIS LOW WING CONFIGN. THIS COULD JUST AS EASILY HAVE BEEN A HIT AS A MISS. WE WERE JUST LUCKY. THERE IS NO EXCUSE FOR THIS. ALL AIRPLANES NEED TO HAVE AND USE TRANSPONDERS!