MAINTAINING MINIMUM CLOUD CLRNC BELOW THE CEILING WHILE STAYING CLR OF THE PDK CLASS D; A PA28 PLT NOTES A TWIN ENG ACFT DSND OUT OF THE CLOUDS 500 FT AHEAD AND PROCEEDING TOWARD THE ARPT.

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I WAS IN LEVEL CRUISE FLT AT APPROX 3800 FT MSL (500+ FT BELOW THE CEILING); ABOUT 10 NM N OF PDK HDG W. KNOWING THAT PDK IS A BUSY CLASS D ARPT WITH A CONSIDERABLE AMOUNT OF JET AND TURBOJET TFC; I WAS FOCUSING MOST OF MY TFC SCAN ON MY L SIDE OF MY ACFT LOOKING FOR ANY DEP TFC. AS I GLANCED TO MY R TO CHK FOR TFC; A TWIN ENG ACFT DROPPED THROUGH IMC AND CROSSED MY FLT PATH. THE TWIN CROSSED MY FLT PATH AT A DISTANCE THAT I ESTIMATED APPROX 500 FT AHEAD OF; AND 250 FT ABOVE; MY ALT. NO EVASIVE ACTIONS WERE REQUIRED ON MY PART; ALTHOUGH I PROBABLY MADE AN INSTINCTIVE TUG TO THE R ON THE YOKE. THE TWIN; AFTER CLRING MY FLT PATH; CORRECTED SLIGHTLY TO THE L. I COULD NOT TELL IF THIS WAS A RESPONSE TO A PRIOR EVASIVE TURN THAT I DID NOT SEE; OR IF IT WAS SIMPLY THE TWIN ALIGNING WITH THE RWY ONCE IN VMC. I DID NOT FEEL THAT EITHER ACFT WAS IN IMMEDIATE DANGER. HOWEVER; THERE WAS THE POTENTIAL FOR AN INCIDENT HAD THE TWIN DROPPED THROUGH THE CLOUDS CLOSER TO MY ACFT. IT CERTAINLY HAD THE POTENTIAL TO BE A CLOSER CALL. CONTRIBUTING TO THIS POTENTIAL NMAC WAS THE FOCUS OF MY TFC SCAN FOR DEP TFC FROM THE NEAR ARPT. I PERCEIVED (INCORRECTLY) THAT THIS WAS WHERE ANY TFC WOULD BE COMING FROM. ALSO CONTRIBUTING TO THIS EPISODE WAS THE SEPARATION DISTANCE FROM THE CLOUD BASES. ALTHOUGH I WAS MAINTAINING A GREATER THAN MINIMUM SEPARATION; HAD I MADE ADDITIONAL ALLOWANCES IN THE VICINITY OF THE BUSY ARPT; I WOULD HAVE HAD A GREATER CUSHION TO SPOT TFC. A THIRD CONTRIBUTING FACTOR WAS MY LOW FLT HRS IN THE ACFT TYPE AND LOW FLT TIME IN THE PAST 90 DAYS. IF NOTHING ELSE; MORE TIME IN TYPE AND MORE FLT TIME WOULD ALLOW A GREATER COMFORT FACTOR WHEN NAVING NEAR HIGH TFC AREAS. FROM THIS POTENTIAL NMAC; I LEARNED THAT I SHOULD NEVER ASSUME THAT I KNOW WHERE TFC WILL BE COMING FROM. ALSO; I LEARNED THAT IN HIGH TFC AREAS; I SHOULD ALLOW MUCH MORE THAN THE MINIMUM REQUIRED CLOUD SEPARATION. FINALLY; I LEARNED THAT I SHOULD BE MORE VIGILANT WITH SCANNING FOR TFC; ESPECIALLY WHEN FLYING ACFT IN WHICH I HAVE LESS FAMILIARITY.