Date: 201204
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Aircraft: Citation Excel (C560XL)
Operator: Fractional
Operating under: Part 91
Flight plan: IFR
Flight phase: Descent
Airspace: Class E ZZZ
ATC / advisory: TRACON ZZZ
Second aircraft: P180 Avanti
Reporter organization: Government
Reporter function: Departure; Approach
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Workload; Situational Awareness; Confusion
Anomaly: ATC Issue All Types; Conflict Airborne Conflict
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: I have not seen a replay of this event; but I will; as it is the single worst incident I have ever been responsible for as a controller! I was working Airport North after I was instructed to close AR7 and combine it with Airport North. AR8 was also combined with Airport North. There was more than the usual amount of traffic from the Northeast going to the West satellites since there is a sporting event this weekend. The controller I relieved had decided to let a slow prop from the Northeast go direct to GKY at 4000 in order to save him 15-20 flying miles. The problem was that he was slow and most of my airspace only has 2 IFR altitudes 3 and 4000; so he was basically near DAL and in the way when the next wave of arrivals converged on DAL. We were running instrument approaches and the arrivals into DAL were hard to sequence since the B737's arriving from the Southwest come in on the approach over the top of DFW and as a controller you have no control of their speed. You ask that they maintain 170kts to the FAF but sometimes they slow to 140kts. So I was very busy working final into DAL threading the needle between approaches to Runway 13R and other ILS approaches to Runway 13L; avoiding the slow over flight that was in the way at 4000; coordinating with ZFW about an unusual departure to the Northeast as usually they are either assigned East or North; dealing with a MU2 that departed off of ADS and would not tag up because his transponder was off by 1 digit even though he swore it was on the correct code; plus I had a head on situation up on the North airway with a DTO arrival that I was working that's supposed to descend from 11-12;000 to 4000 in 15 miles but I had to stop him at 6000 since there was an opposite direction at 5000. While I was dealing with all of this; ZFW yelled at me to take a hand off of 2 aircraft approaching my boundary from the NNE. These 2 aircraft were a C56X above a P180 and their data tags were right on top of each other. My plan was to let the high one continue on the STAR and go Westbound while vectoring the low one Southbound and descend him and that's what I thought my instructions were but a few seconds later the Conflict Alert sounded and Citation was descending into P180. As I was prying them apart I was thinking 'what the hell happened'! As stated earlier I have not seen a replay of the event but my 'assumption' is that I gave Citation; the high aircraft; P180's; the low aircraft; instructions. They got very close together and I assume everyone in the TRACON saw it. I know the operations manager saw it as he was 3 feet away watching on the next scope. I'll say it again; I don't know why it happened but my assumption is that I was so busy that I got those 2 aircraft mixed up and descended the high one by mistake. Several of my co-workers tried to console me by saying 'hey that happens' but it has never happened to me! In my many years as a controller I have made some wrong calls but until today I have never had a 'what the hell' moment where I didn't know why separation was lost! I need to make sure that the aircraft I'm giving instructions to is the correct aircraft. Has never happened before and I need to make certain it never happens again. Also if ZFW could sequence fast props with jets and not put them on top of each other that would help as we don't have much airspace up there.




Synopsis: TRACON Controller described a conflict event when incorrect descent instructions were issued to aircraft on top of another; the controller believe instructions were being issued to the lower aircraft.