Narrative:

An E145 was leading a crj on left downwind for sils approach to runway 21L. I meant to give the crj a 030 heading to straighten out his downwind but I mistakenly said 300 instead. When I realized my error; I intended to reverse the order and make the crj number one for the approach so I widened him out slightly to a 360 heading. I also turned the E145 to a 330 heading to allow more room to insert the crj into the gap. Because the crj was now fairly close to a C441; already on the approach; I instructed the C441 to descent immediately to 5;000 and join the glide slope there. Both the C441 and the E145 read back the descent. I then clarified that the descent was only for the C441. Due to the crj's excessive speed; I now had a conflict between the crj on a 360 heading and the E145 heading. I assigned the E145 an immediate right turn to 360 which he acknowledged. I then turned the crj to a 300 heading and issued traffic. The E145; after acknowledging the immediate right turn; then read back the left turn intended for the crj. I did not catch this read back error. Seeing the aircraft were still converging I realized that the crj had not taken his 300 degree vector and was still northbound so I turned him further right in order to pass behind the E145. The crj did not respond to my vector at first so I repeated it. At this point the E145 was descending from 5;900 to 5;800 so I mistakenly believed that he was still descending to 5;000 from when he took the C441's descent clearance. I elected to let him continue to 5;000 to achieve altitude separation with the crj. The E145 then queried about what altitude I wanted him at and I saw that he had climbed back to 6;000. I descended him to 5;000 and turned him to join the localizer. I then resumed vectoring aircraft in sequence to runway 21L. There were no further incidents. The actions of the flm in the area during this incident were commendable. Although he could see that things were going wrong; he resisted the urge to give instructions that might further complicate a bad situation. We discussed the incident afterward and concurred that while a less experienced controller may have benefited from more direction; the best course of action in this case; given my experience; was to stand ready to provide assistance and allow me to work through the problem. He ensured that the feeder controller did not allow any more airplanes to enter my airspace. He assigned another cpc to plug in with me and make sure that I was not confusing call signs; this was after the only read back error. I was aware that he was at my side if I needed him. The arrival coordinator (C2) was coordinating with adjacent sectors to make sure they were aware of any aircraft that might impact their airspace. This is one of those combinations of human errors that result in a less than desirable situation. There is not much I could have; or would have; done differently. But; I will try to address the issues. The first erroneous vector was a simple mistake. Not much you can do about true mistakes. The missed read back was another error on my part. Obviously; I need to pay more attention to read backs. I assumed that the crj was still descending to 5;000. I should have confirmed that; or actually assigned the altitude rather than making that assumption. I may have clipped a call sign or two when my adrenaline kicked up. Things seemed to go better when I started speaking more slowly and deliberately at the end. I need to control my speech rate even during high pressure situations.

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Original NASA ASRS Text

Title: D21 Controller described a complicated set of events that led to this separation error; listing read back errors; faulty vectors and radio discipline as contributing factors.

Narrative: An E145 was leading a CRJ on left downwind for SILS approach to Runway 21L. I meant to give the CRJ a 030 heading to straighten out his downwind but I mistakenly said 300 instead. When I realized my error; I intended to reverse the order and make the CRJ number one for the approach so I widened him out slightly to a 360 heading. I also turned the E145 to a 330 heading to allow more room to insert the CRJ into the gap. Because the CRJ was now fairly close to a C441; already on the approach; I instructed the C441 to descent immediately to 5;000 and join the glide slope there. Both the C441 and the E145 read back the descent. I then clarified that the descent was only for the C441. Due to the CRJ's excessive speed; I now had a conflict between the CRJ on a 360 heading and the E145 heading. I assigned the E145 an immediate right turn to 360 which he acknowledged. I then turned the CRJ to a 300 heading and issued traffic. The E145; after acknowledging the immediate right turn; then read back the left turn intended for the CRJ. I did not catch this read back error. Seeing the aircraft were still converging I realized that the CRJ had not taken his 300 degree vector and was still northbound so I turned him further right in order to pass behind the E145. The CRJ did not respond to my vector at first so I repeated it. At this point the E145 was descending from 5;900 to 5;800 so I mistakenly believed that he was still descending to 5;000 from when he took the C441's descent clearance. I elected to let him continue to 5;000 to achieve altitude separation with the CRJ. The E145 then queried about what altitude I wanted him at and I saw that he had climbed back to 6;000. I descended him to 5;000 and turned him to join the localizer. I then resumed vectoring aircraft in sequence to Runway 21L. There were no further incidents. The actions of the FLM in the area during this incident were commendable. Although he could see that things were going wrong; he resisted the urge to give instructions that might further complicate a bad situation. We discussed the incident afterward and concurred that while a less experienced controller may have benefited from more direction; the best course of action in this case; given my experience; was to stand ready to provide assistance and allow me to work through the problem. He ensured that the Feeder Controller did not allow any more airplanes to enter my airspace. He assigned another CPC to plug in with me and make sure that I was not confusing call signs; this was after the only read back error. I was aware that he was at my side if I needed him. The Arrival Coordinator (C2) was coordinating with adjacent sectors to make sure they were aware of any aircraft that might impact their airspace. This is one of those combinations of human errors that result in a less than desirable situation. There is not much I could have; or would have; done differently. But; I will try to address the issues. The first erroneous vector was a simple mistake. Not much you can do about true mistakes. The missed read back was another error on my part. Obviously; I need to pay more attention to read backs. I assumed that the CRJ was still descending to 5;000. I should have confirmed that; or actually assigned the altitude rather than making that assumption. I may have clipped a call sign or two when my adrenaline kicked up. Things seemed to go better when I started speaking more slowly and deliberately at the end. I need to control my speech rate even during high pressure situations.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.