LACK OF PROPER GND PLT COORD PRIOR TO EXERCISING PARACHUTE JUMPING ACTIVITY. JUMPERS FELL THROUGH AIRSPACE OCCUPIED BY LOW LEVEL ACFT.

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ON OCCASION WE DROP A PLANE-LOAD OF SKYDIVERS INTO A LARGE FIELD CLOSE TO ONE OF THE SKYDIVER'S HOMES. WE ARE A BUSY DROP ZONE WITH A NUMBER OF PLTS AND A NUMBER OF ACFT. FOR THIS PARTICULAR DROP; I FOUND OUT MINS BEFORE TKOF THAT I WAS TO FLY THE LOAD IN QUESTION. WHEN I ASKED ON THE WAY TO THE ACFT 'NOTAMS FILED; WE SQUARED AWAY FOR THIS JUMP?' THE PERSON COORDINATING THE JUMP SAID 'ALL SET; EVERYTHING'S LEGAL.' MY FIRST MISTAKE WAS NOT VERIFYING WITH FLT SVC THAT A NOTAM HAD IN FACT BEEN FILED. I WAS CONCERNED ABOUT GETTING THE PLANE IN THE AIR ON SCHEDULE; TO ENSURE ALL JUMPERS WERE ON THE GND BEFORE SUNSET. MY SECOND MISTAKE INCLUDED NOT BEING EXPLICIT ABOUT THE LOCATION OF THE DROP. PRIOR TO EVERY DROP; WE PROVIDE A '1 MIN ADVISORY' TO ATC; AND IN RETURN ARE PROVIDED AN ADVISORY OF THE LOCATION OF ALL ACFT IN A 5 NM RADIUS. BASED ON THIS TA; WE PERIODICALLY ABORT A JUMP RUN; AND MAKE AS MANY REPEAT PASSES AS ARE NECESSARY TO ENSURE A SAFE DROP. BASED ON MY BELIEF THAT A NOTAM WAS FILED; AND CONTINUAL RADAR ADVISORIES FROM ATC; I BELIEVED WE WERE SET FOR A CLR DROP -- ALL TFC CALLED OUT BY CTR WAS WELL AWAY FROM OUR POS; AND THE '1 MIN' ADVISORY AND RESPONSE CONFIRMED THIS. JUMPERS LEFT THE ACFT ON THE SECOND PASS (FIRST PASS ABORTED; DUE TO JUMPER REQUEST); AFTER A SECOND '1 MIN' CALL AND TA. WHEN THE ACFT WAS CLR; I CALLED 'JUMPERS AWAY; DSNDING' TO BOTH ZID AND DAY APCH. SOON AFTER MY RETURN TO THE ARPT; I LEARNED 1) PEOPLE ON THE GND HAD WITNESSED LOW LEVEL AIR TFC AROUND THE TIME OF THE JUMP; AND 2) A NOTAM HAD NOT BEEN FILED. I AM CERTAIN THAT I WOULD NOT BE WRITING THIS RPT IF I HAD DELAYED A COUPLE MINS TO CONFIRM THE FILING OF THE NOTAM; OR HAD DISCUSSED OUR INTENTIONS WITH DAY APCH MORE CLRLY; INSTEAD OF ASSUMING; 'ALL SET; EVERYTHING'S LEGAL;' LIKE IT USUALLY IS.