NMAC BTWN A C172 ON DEP OVER A UNCTLED TFC PATTERN AND A MOONEY DEPARTING FROM THE ARPT CLBING UP THROUGH THE RPTR'S FLT PATH.

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I WAS CLRED FOR A HYDE DEP OUT OF THE CLASS B AIRSPACE FROM ANDREWS ENRTE TO MARYLAND ARPT AND TO MAINTAIN 1400 FT. AS I WAS NEARING HYDE FIELD FROM THE N; I NOTICED A MOONEY DEPARTING RWY 23 (W32). I WATCHED THE MOONEY CLOSELY AND FLEW A COURSE TO THE R OF THE MOONEY TO SEE WHAT IT WOULD DO. AT THAT POINT; I NOTED MY ALT TO BE ABOUT 1500 FT; I DSNDED IMMEDIATELY TO 1400 FT. SHORTLY AFTERWARD; THE MOONEY MADE AN ABRUPT TURN TO R XING MY COURSE. I TURNED L BEHIND HIM SEEING THERE WAS MORE THAN AMPLE ROOM. I WOULD HAVE ALTERED COURSE FURTHER W (R) AS PER RIGHT OF WAY RULES EXCEPT I HAD BEEN CONCENTRATING ON THE MOONEY; NOT SO MUCH MY ALT OR AIRSPACE TO MY R. SO; I WAS WORRIED I HAD MISSED AN ACFT COMING INTO OR DEPARTING NEARBY POTOMAC AIR PARK (ABOUT 1 1/2 MI W). I HAVE TO SAY I DOUBT IF THE CTLR SAW THE MOONEY ON HER SCOPE. SHE NEVER SAID A WORD ABOUT MY MANEUVERING AND SHE DID NOT DUMP ME AT THE EDGE OF THE CLASS B CUTOUT LIKE OTHERS HAVE DONE TO ME. I AM REASONABLY SURE THE MOONEY NEVER SAW ME.