ZMA CTLR EXPRESSED CONCERN REGARDING AN ALLEGED PROCEDURAL CONFLICT BETWEEN ACFT DEP MIA TRACON AIRSPACE.

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THERE IS A BUILT IN CONFLICT DEPARTING MIAMI APPROACH ON THE PREDA AND VALLY TRANSITIONS. PREDA IS USED FOR AIRCRAFT DEPARTING FLL & FXE AND FLYING SOUTH; SOUTHEAST BOUND. VALLY IS USED FOR MIA DEPARTURES FLYING NORTH; NORTHEAST BOUND. THE PREDAS ARE ASSIGNED A 090 HEADING AND THE VALLYS ARE FLYING A 060 HEADING; BOTH CLIMBING TO 16;000. AIRCRAFT LOSE MINIMUM SEPARATION APPROXIMATELY 5-7 MILES IN MIAMI CENTER'S AIRSPACE. MOST OF THE TIME THE APPROACH AND CENTER CONTROLLERS WILL TRY AND COORDINATE ALTERNATE ACTIONS TO PREVENT LOSS OF SEPARATION; BUT THAT IS NOT ALWAYS POSSIBLE DEPENDING ON WORKLOAD. IN THE EVENT OF LOSS OF COMMUNICATION WITH ONE OR BOTH AIRCRAFT; THERE IS NO WAY TO PREVENT AN OPERATIONAL ERROR; A NMAC; OR WORSE. THIS PROCEDURE HAS BEEN IN PLACE FOR MANY YEARS AND HAS NOT BEEN AN ISSUE. WITH THE INCREASE IN TRAFFIC THE PAST FEW YEARS; THIS SCENARIO IS OCCURRING SEVERAL TIMES A DAY. A POSSIBLE CORRECTION TO THIS PROBLEM WOULD BE TO HAVE THE PREDA DEPARTURES STOPPED AT 13000 FT AND GIVE MIAMI CENTER CONTROL FOR HIGHER ON CONTACT. THIS SUGGESTION HAS BEEN PRESENTED TO MIAMI CENTER'S AIRSPACE OFFICE WITH NO ACTION TAKEN TO RESOLVE THE PROBLEM.