A C172 PILOT FLEW DIRECTLY UNDER A SAILPLANE WITH 300 FT VERTICAL CLEARANCE.

Narrative

WHILE CRUISING AT 4500 FT BTWN DMW AND FDK; I SAW A GLIDER THAT APPEARED TO BE CIRCLING AT 12 O'CLOCK POS; SEVERAL HUNDRED FT ABOVE ME; SEVERAL MI AHEAD. AS I APCHED; I WATCHED IT CLOSELY. I DETERMINED THAT IT WAS IN FACT CIRCLING IN A STEADY PATH WITHOUT ANY DECREASE IN ALT; AND I DECIDED THAT THERE WAS ENOUGH ROOM THAT I COULD SAFELY PASS UNDERNEATH WITHOUT CHANGING ALT OR TAKING OTHER EVASIVE ACTION. WHILE I WAS READY TO DIVE IF NECESSARY; I HELD MY ALT; AND I CONTINUED TO CLOSELY WATCH THE GLIDER UNTIL IT DISAPPEARED ABOVE ME. I BRIEFLY SAW THE GLIDER THROUGH THE SMALL ROOF WINDOWS OF THE PLANE AS I PASSED UNDERNEATH IT. I ESTIMATE THAT I WAS APPROX 200-300 FT FROM THE GLIDER WHEN I PASSED UNDERNEATH IT. WHILE MY ATTN AT THE TIME HAD BEEN FULLY DEVOTED TO MAKING SURE THAT I COULD SAFELY PASS UNDERNEATH THE GLIDER; IN RETROSPECT; I REALIZE THAT THE GLIDER PLT HAD NO WAY OF KNOWING THAT -- AND I PROBABLY GAVE HIM OR HER A SERIOUS SCARE AS A RESULT. I WAS PROBABLY TOO CLOSE FOR COMFORT; AND IT CREATES AN OPEN QUESTION OF WHETHER I WAS 'WELL CLR' OF THE OTHER ACFT; AS REQUIRED BY THE FAR'S -- ESPECIALLY IN LIGHT OF THE FACT THAT THE GLIDER HAD THE RIGHT-OF-WAY. IN THE FUTURE; EVEN IF I THINK THAT I CAN SAFELY PASS ANOTHER NEARBY ACFT WITHOUT TAKING EVASIVE ACTION; I WILL DO SO WITH AT LEAST 500 FT OF SEPARATION; AND PREFERABLY MORE. I WILL ALSO CHANGE POS OR ALT IN A WAY THAT IS VISIBLE TO ANOTHER PLT; SO THAT HE OR SHE CAN SEE THAT I AM; IN FACT; PAYING ATTN. NOT ONLY WILL THAT KEEP ME FROM CAUSING ANOTHER PLT TO BE CONCERNED; AS I PROBABLY DID IN THIS CASE; BUT IT WOULD ALSO GIVE ME A LARGER BUFFER ZONE IN THE EVENT OF ANY UNEXPECTED CHANGES IN PATH; POS; OR ALT THAT MIGHT RESULT IN A COLLISION.