Date: 201508
Local time of day: 1801-2400
Location: HCF.TRACON, HI
Light: Night
Aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class E HCF
ATC / advisory: TRACON HCF
Second aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Reporter organization: Government
Reporter function: Approach
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Communication Breakdown; Confusion; Situational Awareness; Training / Qualification
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Provided Assistance
Contributing factors: ATC Equipment / Nav Facility / Buildings; Procedure; Human Factors; Airspace Structure
Primary problem: Procedure

Narrative: I was working R5 combined with D5 when I issued Aircraft X a visual approach to Runway 17 at KOA airport. KOA airport is served by a contract tower and as such has absolutely no authority to provide radar service to any aircraft. After vectoring Aircraft Y off of its assigned routing to achieve the proper spacing to follow Aircraft X; I then cleared Aircraft Y for an ILS Runway 17 approach with Aircraft Y approximately 7-8 miles in trail of Aircraft X to Runway 17. I switched Aircraft X to KOA tower frequency about 15 miles from the airport. I then proceeded to update and 'stuff' my flight progress strips. When I turned my attention back to the radar scope; I noticed that Aircraft X was now proceeding directly eastbound across final and not towards the airport. This resulted in a rapidly decreasing amount of separation between this now eastbound Aircraft X and the Aircraft Y that was inbound on the localizer course. I proceeded to call traffic to Aircraft Y and this aircraft reported the Aircraft X in sight. I then recleared Aircraft Y for a visual approach to Runway 17 with the restriction to follow Aircraft X. I then called the supervisor over to observe what was occurring. The supervisor noted that it appeared that KOA tower may have turned Aircraft X to follow a VFR aircraft that was inbound to KOA. Next I measured the distance between these 2 aircraft and now there was less than 5 miles.   After being relieved from position I discussed this situation with the supervisor and he relayed to me that he had talked to the 'controller' at KOA tower. The KOA controller said he turned Aircraft X because a VFR Cessna checked in on tower frequency 'kind of late'. The KOA controller tried to explain his actions and justify what he did by stating that he had both Aircraft X and Aircraft Y in sight.  This is absolutely irrelevant in the fact that KOA tower has absolutely no authority to ever vector or slow down (both require radar qualification) an IFR aircraft. As is obvious in this situation; the reason being that it may result in a loss OF IFR separation to subsequent aircraft that are also inbound to the airport.These types of occurrences have been happening at KOA tower for years. If the FAA was really interested in safety and efficiency of flight; then they would make the airspace around KOA a Class C. They would install an ASR radar; hire radar qualified controllers to staff KOA tower; and establish an approach control sector to work the traffic. But instead; they develop DVA's [Diverse Vector Areas] that do not meet any of the criteria necessary for creating DVA's and insist that radar procedures can be used when the radar being used at KOA is an ARSR with no primary radar capabilities.    Also; the controllers at KOA tower need to be briefed that they are not now; nor will they ever be in the near future allowed to provide radar service to aircraft.




Synopsis: HCF Controller described a situation where the KOA Tower Controller vectored an aircraft to avoid another. KOA controllers are not allowed to provide vectors and this led to a loss of separation with an inbound aircraft.