NMAC. 2 ACFT APCHING ARPT FROM DIFFERENT DIRECTIONS AND UNDER DIFFERENT CTLR; RPTR ACFT (HELI) CTLED BY TWR AND OTHER ACFT UNDER APCH CTLR. THOUGH BOTH ACFT HAD VISUAL WITH EACH OTHER; RPTR BELIEVED THEY WERE TOO CLOSE IN THE PATTERN AND TOOK EVASIVE ACTION.

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ACFT #1 ENRTE FROM NW DIRECT TO HELIPAD SSE OF ARPT; INITIALLY AT 1200 FT MSL. ACFT #1 BEING WORKED BY APCH CTL. ACFT #2 APCHING ARPT FOR LNDG ON RWY 1. ACFT #2 WORKED BY TWR CTLR. EACH ACFT HAD THE OTHER IN SIGHT. DUE TO IT BEING AT NIGHT; THE DARKNESS MADE IT DIFFICULT TO JUDGE DISTANCE AND FLT PATH. WHEN ACFT #1 REALIZED THEIR FLT PATHS WOULD CROSS IN PROX TO EACH OTHER; ACFT #1 DSNDED TO APPROX 800-900 FT MSL; EVENTUALLY XING UNDER ACFT #2. DUE TO THE DIFFICULTY OF JUDGING THE FLT PATH OF ACFT #2 AT NIGHT; THE DSCNT APPEARED TO BE THE SAFEST; AS A L TURN MAY HAVE BEEN INTO #2'S FLT PATH AND A R TURN MAY HAVE PLACED THE HELI IN ACFT #2'S WAKE TURB. FACTORS WHICH WOULD HAVE HELPED INCLUDE HAVING BOTH ACFT ON THE SAME FREQ SO THAT EACH PLT AND CTLR COULD HEAR THE OTHERS FOR PURPOSES OF WHAT EACH OTHER SEES AND/OR PERCEIVES. ALL SHOULD BE ON 'TWR' IN THE ATA AND ON 'APCH' IN THE CLASS C. ALSO A BETTER METHOD TO CROSS ACFT FROM ONE SIDE OF AN ARPT TO THE OTHER; ACROSS APCH/TKOF PATHS WHILE TFC IS LNDG OR DEPARTING; WOULD BE OVER THE CTR OF THE ARPT. THIS WOULD KEEP POTENTIALLY CONFLICTING ACFT OUT OF THE APCH AND TKOF CORRIDORS; PLACING THEM OVERHEAD; WHEREAS THE LNDG/TKOF ACFT WOULD BE ON THE GND.