Narrative:

Emb-145 was inbound to cid; level at 11;000; 40 NM east of the airport. On initial contact; I advised emb-145 to proceed direct cobvo for the RNAV runway 26 approach; and to expect lower in five miles. This was the only aircraft I had on my frequency. At that time I was observing two targets; one squawking 1;200 and indicating 7;500 MSL and the other a primary target; apparently a flight of two aircraft heading southeast-bound well ahead of emb-145. The tracks did appear likely to converge. After emb-145 crossed our airspace boundary with mli approach; 35 NM east of cid; I gave the pilot; 'pilot's discretion descent to 2;700;' and issued the traffic at one o'clock; 15 miles. Emb-145 advised they were looking into the sun and the traffic would be difficult to spot. Emb-145 then began descent out of 11;000 MSL. When the aircraft were about 5 NM apart; with emb-145 descending through approximately 8;200; I issued the traffic again; at twelve o'clock and five miles. The emb-145 pilot advised they did not have the traffic in sight; but did have it on TCAS. Emb-145 continued to descend; although slowly; I thought they were leveling at 8;000 MSL; but then continued down. As emb-145 descended through about 7;700 MSL; the mode C intruder alarm sounded. As the targets were approximately 1 mile apart; and emb-145 was reaching 7;600 MSL; the pilot advised he was responding to a TCAS RA climb. I responded; 'roger.' as emb-145 reached approximately 7;800-7;900 MSL; they began leveling and the pilot advised me the RA was complete and that he had the two targets in sight. He identified them as a pair of cessna C150s; about 1/2 mile apart. Continued descent and landing at cid occurred without incident. I have a couple of thoughts. First; from the controller side; I could have been more urgent in my traffic calls; specifically saying the tracks were converging. I actually intended to do this; but once the pilot advised he had the targets on TCAS; I decided not to. Secondly; I could have issued a traffic alert; but again I knew the pilot had the targets on TCAS; and I knew I had assigned pilot's discretion descent. I assumed with those two factors; the pilot could adjust his descent or make a better decision from the cockpit than my issuing an immediate climb or turn. Another thought I had was; the pilot's choice in descending. He had had 15 miles notice of the traffic and its indicated altitude; then was tracking it via TCAS as they got closer. It seems odd from my viewpoint that he would choose to continue to descend to the indicated altitude of the traffic. True; indicated altitude is not verified altitude. Not being a pilot myself; nor having access to flight decks anymore due to the loss of the familiarization flight program; perhaps the pilot felt confident in the view out the window given the TCA/traffic advisory information he had. I will say many other controllers at my facility would have only issued emb-145 descent to 8;000 MSL; or given a vector around the traffic; without the pilot's request; rather than direct to cobvo. I also know the .65 does not require either of these actions; in fact mandating vectors around traffic only when the pilot requests! I also know the VFR traffic's indicated altitude of 7;500 MSL was not verified; therefore an assignment of 8;000 MSL for emb-145 would not have ensured anything. The pilot did not sound worried or concerned at any time during this event. I gave the best traffic information I thought necessary at the time. I do not feel this was a serious event in any way; but just felt a report might be helpful.

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Original NASA ASRS Text

Title: CID Approach Controller reported a TCAS RA event involving an CID air carrier arrival and two targets that indicated 7;500; the reporter detailing reasoning for actions taken and/or not taken.

Narrative: EMB-145 was inbound to CID; level at 11;000; 40 NM east of the airport. On initial contact; I advised EMB-145 to proceed direct COBVO for the RNAV Runway 26 approach; and to expect lower in five miles. This was the only aircraft I had on my frequency. At that time I was observing two targets; one squawking 1;200 and indicating 7;500 MSL and the other a primary target; apparently a flight of two aircraft heading southeast-bound well ahead of EMB-145. The tracks did appear likely to converge. After EMB-145 crossed our airspace boundary with MLI approach; 35 NM east of CID; I gave the pilot; 'pilot's discretion descent to 2;700;' and issued the traffic at one o'clock; 15 miles. EMB-145 advised they were looking into the sun and the traffic would be difficult to spot. EMB-145 then began descent out of 11;000 MSL. When the aircraft were about 5 NM apart; with EMB-145 descending through approximately 8;200; I issued the traffic again; at twelve o'clock and five miles. The EMB-145 pilot advised they did not have the traffic in sight; but did have it on TCAS. EMB-145 continued to descend; although slowly; I thought they were leveling at 8;000 MSL; but then continued down. As EMB-145 descended through about 7;700 MSL; the Mode C Intruder alarm sounded. As the targets were approximately 1 mile apart; and EMB-145 was reaching 7;600 MSL; the pilot advised he was responding to a TCAS RA climb. I responded; 'Roger.' As EMB-145 reached approximately 7;800-7;900 MSL; they began leveling and the pilot advised me the RA was complete and that he had the two targets in sight. He identified them as a pair of Cessna C150s; about 1/2 mile apart. Continued descent and landing at CID occurred without incident. I have a couple of thoughts. First; from the controller side; I could have been more urgent in my traffic calls; specifically saying the tracks were converging. I actually intended to do this; but once the pilot advised he had the targets on TCAS; I decided not to. Secondly; I could have issued a traffic alert; but again I knew the pilot had the targets on TCAS; and I knew I had assigned pilot's discretion descent. I assumed with those two factors; the pilot could adjust his descent or make a better decision from the cockpit than my issuing an immediate climb or turn. Another thought I had was; the pilot's choice in descending. He had had 15 miles notice of the traffic and its indicated altitude; then was tracking it via TCAS as they got closer. It seems odd from my viewpoint that he would choose to continue to descend to the indicated altitude of the traffic. True; indicated altitude is not verified altitude. Not being a pilot myself; nor having access to flight decks anymore due to the loss of the Familiarization Flight Program; perhaps the pilot felt confident in the view out the window given the TCA/traffic advisory information he had. I will say many other controllers at my facility would have only issued EMB-145 descent to 8;000 MSL; or given a vector around the traffic; without the pilot's request; rather than direct to COBVO. I also know the .65 does not require either of these actions; in fact mandating vectors around traffic only when the pilot requests! I also know the VFR traffic's indicated altitude of 7;500 MSL was not verified; therefore an assignment of 8;000 MSL for EMB-145 would not have ensured anything. The pilot did not sound worried or concerned at any time during this event. I gave the best traffic information I thought necessary at the time. I do not feel this was a serious event in any way; but just felt a report might be helpful.

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.