NMAC BTWN AN SMT DSNDING AND AN MLG CLBING OUT JUST OUTSIDE OF CLASS C AIRSPACE.

Narrative

TOOK THE ACFT OUT TO TEST A NEW WASTEGATE INSTALLED ON R ENG. WAS VECTORED OUT OF CLASS C AIRSPACE TO N AND RADAR SVC TERMINATED. CLBED TO 12500 FT AND SET UP FOR CRUISE ON 320 DEG HDG. GSO WAS LNDG RWY 32 SO DECIDED TO MAKE DSCNT TOWARDS SW QUADRANT TO RE-ENTER CLASS C. WAS ON 200 DEG HDG AND BEGAN DSCNT AND TUNED ATIS FOR RECHK OF CURRENT INFO. COPIED ATIS; ADJUSTED VOR CDI AND LOOKED OUT L WINDOW TO SEE A SILVER AND RED B737 PASS UNDERNEATH ON A WNW HDG. SWITCHED TO DEP AND NO ONE TALKING THERE; TRIED CTR AND HE WAS POINTING OUT ADDITIONAL TFC TO SOMEONE. WENT ON AND CONTACTED APCH FOR RETURN TO GSO. THE 737 HAD PROBABLY JUST SWITCHED TO CTR DURING CLB OUT OF GSO; DON'T KNOW IF THEY HAD DISCUSSED MY TARGET ON 1200 MODE C OR NOT; BUT MY DSCNT MAY HAVE SURPRISED THEM. I SHOULD HAVE BROUGHT A COPLT ALONG TO WATCH OR TUNE RADIOS WHILE I CHKED THE ENG AND NAVED ACFT. SHOULD HAVE TUNED RADIOS WHILE IN LEVEL FLT AND THEN STARTED DSCNT. SHOULD HAVE BEEN LOOKING MORE CAREFULLY FOR TFC. HE CAME FROM BELOW L; CLBOUTS COMING TOWARDS YOU ARE SMALL AND NOT MOVING AGAINST THE BACKGND OF CITIES AND FARMS BELOW. SHOULD HAVE INSISTED ON CONTINUING FLT FOLLOWING WITH APCH EVEN THOUGH I WAS CLBING OUT AND LEAVING CLASS C. NEXT TIME I WILL AT LEAST TAKE ALONG AN OBSERVER TO LOOK OUT WHILE I ADJUST AND CHK THINGS. WILL ALSO STAY IN RADAR WITH SOMEONE WHILE THAT CLOSE IN TO A MAJOR ARPT.