Date: 201904
Local time of day: 1201-1800
Location: ZMA.ARTCC, FL
Flight conditions: VMC
Light: Daylight
Aircraft: Any Unknown or Unlisted Aircraft Manufacturer
Flight plan: IFR
Flight phase: Descent
Airspace: Class E ZMA
ATC / advisory: Center ZMA
Second aircraft: Any Unknown or Unlisted Aircraft Manufacturer
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Distraction; Situational Awareness; Workload; Communication Breakdown
Anomaly: ATC Issue All Types; Conflict Ground Conflict; Critical; Conflict NMAC
Detector: Automation Aircraft RA; Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Issued Advisory / Alert; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Took Evasive Action
Contributing factors: Airspace Structure; Staffing; Company Policy; Human Factors; Procedure
Primary problem: Procedure

Narrative: I was working two combined sectors. I was about an hour into my session and working a ridiculously high volume of traffic; which was equally complex and unsafe. The sector should have been split; with Miles in Trail restrictions to reduce sector volume. The ESIS (Enhanced Status Information System) was borderline at the numbers; between red/yellow/green but was lower than actuality because it does not factor in the numerous VFR aircraft that were on frequency; nor the complexity of the airspace with the military airspace active. The MAP number is unfortunately fixed and does not change with military airspace activation. But if you listen to the tapes; there was not a moment of dead air. The military airspace to my east was previously hot; and had just gone cold a few minutes prior; which had also inherent complexity. A C130 had spilled out of a MOA and was operating in my sector IFR; requesting his IFR clearance. I issued Aircraft X a descent to 3;000 feet from 1;900 feet. Then I went on to other aircraft. At the time of the clearance; I had observed no other aircraft but had serious datablock and sector saturation. About 5 minutes after I issued the clearance; I observed a target at Aircraft X's 12'oclock and 1 mile at 3;300 feet. I immediately issued 'Aircraft X STOP DESCENT.' Aircraft X was out of 4;600 feet approximately. I issued this 3 more times with no response from Aircraft X. As Aircraft X was through 4;000 feet; he said 'Center we're responding to an RA' I never issued traffic; and told Aircraft X 'When Able; Turn 30 degrees left.' Aircraft X never advised clear of conflict; and I said 'When able; descend and maintain 3;000'. He was clear of traffic at that point. The aircraft that he was in conflict with was a VFR on a 1200 code not talking to me. I cannot stress how busy this session was at the time; it was 10/10 and 10/10 complexity.Jet Aircraft arriving PGD should ABSOLUTELY not be descending to 3;000 feet direct PGD from LAL. This has been a reoccurring safety issue over the past 5 years at a rate of approximately 30-50 RA's in this one area alone. The Letter of Agreement with Approach is outdated; unsafe; and requires us to descend our [inbounds] to 3;000 feet approximately 15 miles north of the airport. On every airplane; we have to 'slam dunk' the arrivals from crossing Lakeland at 19;000 feet. They have to be at 19;000 feet because of the Orlando airport underneath them at 13;000 (with arrivals unrestricted from the western sector; they could be in conflict if [the inbound aircraft] was anything lower. Clearing that traffic; we have to vector the arrival around the Tampa approach DTA; Orlando approach DTA; and then across 3 of the Tampa Approach; SRQ; VNC arrival areas; before finally descending them to 3;000 feet and running them at our lowest altitude available to PGD. This is a commonly trafficked area by VFR aircraft to and from all of the southern satellite airports. The majority of these aircraft are not talking to ATC since it's Class E airspace. FAA Management has previously responded to these complaints by putting a NOTAM out; which has no effect.The only solution to these arrivals is that they have to be routed a different way. Either through Approach airspace or another route. There is a route which is the most ideal because most aircraft cannot transit the SRQ/VNC area without talking to ATC due to the Class B and Class C rings around other airports. Putting them east of these rings basically sanctions the aircraft not to talk to anyone while we're dodging them with our jets. Another RNAV Arrival would also make sense since it's a STAR that's being used by Approach traffic. Unfortunately; for as long as I've been here; the FAA has been refusing to make changes to the STAR; develop a STAR or SID for PGD as they say 'it would take too long to implement.' Unfortunately; that cannot be an excuse anymore; we must act before someone has a midair in this vicinity. I didn't mention the departures yet; but those are directly head on with all of the arrivals climbing to 4;000 feet. So there are more than one occasion that you have to give 4-5 vectors to one aircraft to get them through 10;000 feet without hitting traffic.




Synopsis: ZMA Center Controller reported attempting to stop an aircraft's descent at the last minute for VFR traffic; but receiving no response.