Date: 201405
Local time of day: 1801-2400
Location: AUS.Airport, TX
Aircraft: Small Transport
Flight plan: VFR
Mission: Skydiving
Flight phase: Descent
Airspace: Class C AUS
ATC / advisory: Tower AUS
Second aircraft: Small Aircraft; High Wing; 1 Eng; Fixed Gear
Reporter organization: Government
Reporter function: Approach; Departure
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Communication Breakdown; Distraction; Confusion
Anomaly: ATC Issue All Types; Conflict NMAC; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Contributing factors: Aircraft; Procedure
Primary problem: Procedure

Narrative: We have two parachute jumping areas in the southwest corner of our airspace; very near another facilities airspace. Aircraft X advised one minute prior to jumping and I had two aircraft nearing that area; so I turned the first one slightly north to avoid the area. I tried to turn Aircraft Y to the southwest to pass around both jumping areas; with no response; they were still about 7 miles from the jump zone so they were no factor for the jumpers but I was worried the descent of the jump plane after the drop. I tried Aircraft Y again moments later with no response again; so I advised Aircraft X about the traffic that was nearing the airfield they were descending into. I had a high workload at this time so I made several other transmissions then checked back on the situation and at this time Aircraft X was about 300 feet lower than Aircraft Y; the plane typically descends rapidly as they spiral directly down onto the field. I assumed Aircraft X would easily be below Aircraft Y since they were still about 3 miles apart at the time; so I issued the traffic again and allowed them to go to advisory frequency. I then called the adjoining facility to advise them that Aircraft Y was NORDO and they said they were talking to him; shortly after this I noticed Aircraft Y start a sharp descent which brought them within 200 feet of Aircraft X who had seemed to slow his descent. The two planes then turned away from one another and continued onto their respective destinations. When the replay was watched it was noticed that Aircraft Y was never switched to my frequency from the previous facility and I had not noticed due to the volume and complexity of the traffic I was handling at the time; so apparently he had switched to the next facilities frequency on his own skipping my frequency altogether. Part of the problem is that our radar coverage in the southeast of our airspace is very poor; I was not able to radar contact Aircraft Y at the boundary and told the adjacent facility to keep them flying into my airspace and the radar should arts track shortly; Aircraft Y was at 65 feet and had to fly about 10 miles into my airspace before I could slew and take the radar hand off. I believe that because hand offs in that area are often made at a much later time than typical hand offs that it makes it easier for both facilities to forget about them when scanning their airspace.After viewing the replay and thinking about the situation numerous times; I am upset with myself for allowing Aircraft X to change to the advisory frequency and assuming to two aircraft would continue present descent rates. Since I wasn't talking to Aircraft Y I should have held onto Aircraft X until I was sure about the situation. As for the poor radar coverage; we are supposed to be getting STARS in a few months so hopefully that will help the radar coverage.




Synopsis: AUS Controller describes an operational error involving a no radio aircraft and an aircraft that had just dropped parachuter's.