NMAC IN MARGINAL WX CONDITIONS.

Narrative

ANOTHER RATED PLT WAS SEATED IN THE R FRONT SEAT. I LANDED AT ROCKWALL ARPT (F46) AT XA00 LCL TIME; TO PICK UP A PAX. WHEN I LANDED AT ROCKWALL THE CEILING WAS 2300 FT AND VISIBILITY BETTER THAN 10 MI WITH A FORECAST OF FOG AND DRIZZLE FOR SEVERAL HRS LATER. AT APPROX XA43 LCL TIME AND BEFORE DEPARTING ROCKWALL ARPT RWY 16; I TURNED ON THE LNDG LIGHT; NAV LIGHT; BEACON AND STROBE LIGHT. I ANNOUNCED VIA THE UNICOM FREQ 122.8 MY INTENTIONS TO TKOF RWY 16 AND INTENTIONS TO DEPART TO THE W. I TOOK OFF IN A STANDARD TFC PATTERN TO THE S AND AFTER CLRING THE TFC PATTERN S I TURNED TO THE W STILL CLBING. AFTER CLBING OUT; I LEVELED OFF AT 1400 FT MSL AND REMARKED TO MY COPLT THAT THE CEILING AND VISIBILITY DID NOT LOOK SO GOOD AND I WAS GOING TO CLB AND CHK THE CEILING. I CONFIRMED THE CEILING AT 1500 FT MSL AND DSNDED TO 1400 FT MSL WHEN MY COPLT GRABBED THE YOKE; WENT INTO A HARD L TURN AND SLIGHT CLB AND SHOUTED; 'AIRPLANE!' I LOOKED TO MY R WHERE HE WAS LOOKING AND ASKED; 'WHERE?' I NOTICED MY COPLT WAS LOOKING STRAIGHT OUT THE R WING AND DOWN STILL HOLDING A L TURN/CLB. I IMMEDIATELY INCREASED BACK PRESSURE ON THE YOKE TO MAKE A CLR ZONE BELOW US AND LEVELED AT THE CLOUD BASE. I HAVE A RYAN TFC COLLISION ALERT DEVICE. I HAD SET IT FOR TERMINAL MODE FOR TKOF AND HAD NOT HAD TIME TO SET IT FOR STANDARD MODE FOR CRUISE FLT SINCE I DEPARTED ROCKWALL. THE THREAT ACFT PASSED UNDER ME FROM R TO L AND THE TCAD SHOWED HIM TO PASS 100 FT BELOW ME. MY COPLT LATER STATED THE THREAT ACFT; WHEN FIRST OBSERVED; APPEARED TO BE IN A SLIGHT CLB COMING TOWARD US THEN APPEARED TO TAKE EVASIVE ACTION BY LEVELING OFF BUT HE WAS NOT POSITIVE ABOUT THE ATTITUDE OF THE ACFT. WE WERE NOT ABLE TO IDENT THE THREAT ACFT BUT IT APPEARED TO BE A CESSNA SKY HAWK; BLUE AND WHITE. NO LIGHTS WERE OBSERVED ON THE ACFT. THE THREAT ACFT CONTINUED EBOUND. DUE TO THE WX DETERIORATING; I FELT THIS FLT WAS NO LONGER SAFE AND MADE AN UNEVENTFUL LNDG AT ROCKWALL ARPT. PREVENTION: THE THREAT ACFT SHOULD HAVE KNOWN HE WAS PASSING 2 MI OF AN ARPT AND SHOULD HAVE MONITORED THE UNICOM FREQ. THE THREAT ACFT SHOULD HAVE DISPLAYED ALL LIGHTS UNDER EXISTING METEOROLOGICAL CONDITIONS. IF TCAD HAD BEEN SET FOR STANDARD IMMEDIATELY ON DEP; I WOULD HAVE BEEN AWARE OF THE THREAT AIRPLANE WHEN HE WAS 2 MI AWAY FROM ME.