Date: 201908
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Light: Daylight
Aircraft: Regional Jet 200 ER/LR (CRJ200)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class C ZZZ
ATC / advisory: TRACON ZZZ
Second aircraft: Skyhawk 172/Cutlass 172
Reporter organization: Government
Reporter function: Instructor; Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness; Training / Qualification; Communication Breakdown; Confusion
Second reporter function: Approach
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew; Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Air Traffic Control Separated Traffic; Flight Crew Executed Go Around / Missed Approach
Contributing factors: ATC Equipment / Nav Facility / Buildings; Procedure; Human Factors
Primary problem: Procedure

Narrative: I was the OJTI (On-the-Job Training Instructor) in a training session on LC (Local Control). The Supervisor had just released control of our ASR 8 radar to tech ops to perform repairs. This meant we were going to lose our single sensor abilities but stay in Fusion mode. We were given less than 15 minutes notice of the outage and it was unclear what procedures we were supposed to be following. We were then told to follow 'CENRAP' (Center Radar Presentation) procedures which no longer existed since we were now operating under STARS/Fusion. The CENRAP procedures button on the IDS (Information Display System) had been removed; so our quick reference was gone. Subsequently; everyone was trying to guess/remember what the CENRAP procedures entailed. Part of this was passing inbounds to the Tower. Radar forgot to pass an inbound (Aircraft X) and he subsequently dropped off radar and Radar forgot about him. He dropped off early enough that we never saw him on final on our radar depiction. When Radar discovered the missing aircraft; they called us on LC asking if we knew where he was; we replied negative and started searching visually for him. Meanwhile; Aircraft Y was in the pattern and had turned base in direct conflict with Aircraft X. Aircraft X and Aircraft Y saw each other and initiated action to avoid each other. Aircraft X made a right turn and initiated a go around while Aircraft Y made a left turn to a crosswind.Everyone needs to be fully aware what procedures are being implemented during a major equipment outage. All controllers should have been advised to refresh themselves on our ASR 8 outage procedures in the SOP via pre-duty CEDAR message or via face to face Supervisor briefing. Using deprecated terms like 'CENRAP' to describe what we should be doing is a disservice since those procedures are no longer in effect; are no longer taught; and cause uncertainty; ambiguity; and speculation about what we're supposed to be doing. Even with our last minute notice; being told to follow the ASR 8 outage procedures per the SOP would have been much better than to say we're following CENRAP procedures; so at least we know where to look up what we should be doing.


Second narrative: While working Radar East position; Management scheduled an ASR-8 outage for maintenance. We were told we'd be working a modified 'CENRAP' (Center Radar Presentation) using long range radars and ADSB for separation; that 5 miles of separation applied with different MVA's (Minimum Vector Altitudes) but not much more. While working this modified CENRAP; I got Aircraft X inbound for landing. He called the field in sight so I cleared him for the visual and began discussing the procedures for this 'modified CENRAP' with the Controller in Charge. We weren't sure if we should call aircraft inbound; or if I should terminate radar on IFR aircraft even if I could still see them or what exactly should be happening. During the course of this conversation I lost radar on Aircraft X but thought that I'd already switched him to Tower. The CIC double checked to which the tower reported no knowledge of Aircraft X and they were not talking to him. I reached out for Aircraft X and he was still on my frequency. I asked Aircraft X to say position to which he only responded short final. I could see Tower had one aircraft in the pattern on final but could not determine if Aircraft X and the unknown aircraft would be factors for each other. I asked Aircraft X if he could maintain terrain and obstruction clearance in a climb to 6;000 ft. to which he said he could so I climbed him and turned him to a 080 to ensure separation to the best of my abilities. We were 'flying by the seat of our pants' in the radar room. There was no briefing even though this was a scheduled outage. After the event; Upper Management released a CEDAR blurb of an SOP entry regarding CENRAP which could have been helpful prior to the event but was hardly helpful after. This should be briefed prior to the outage when it is scheduled.


Synopsis: Air Traffic Controllers reported a radar outage without adequate warning that resulted in airborne conflict between two aircraft.