Narrative:

Aircraft X; a LJ35; was on course to bearz intersection for pwk. When I issued a descent to 4;000 ft for aircraft X; I failed to change his frequency to my low altitude frequency; which led to complications later. Aircraft Y; a C550; was also on course for pwk over bvt then bearz intersection. Aircraft Y was much slower than aircraft X and thus the plan was to turn aircraft Y east until he was far enough behind aircraft X for required spacing; and then turn him to bearz. I also failed to put aircraft Y on my low altitude frequency when I issued a descent to 4;000 ft. Aircraft X cut through sbn approach airspace on his way to bearz; thus; he was pointed out to the sbn controller descending towards bearz. As the aircraft approached my boundary with C90; it was time to turn aircraft Y to a 090 heading so he would fall behind aircraft X; however; when I issued the clearance; I inadvertently used the abbreviated call sign [for] aircraft X instead of aircraft Y. Because the aircraft was not properly placed on my low altitude frequency; the pilot heard my clearance and took it; but I was unable to hear his communication back to me when he read back the clearance. Thus; aircraft X took the clearance and turned eastbound further into sbn approach airspace at 4;000 ft. I called sbn controller and advised them of the situation and they advised that the aircraft was 'still point out approved.' I then turned aircraft Y to a 090 heading and called C90 to work out a plan. They advised me to put aircraft Y on a north heading and that he was radar contact. When I tried to contact aircraft Y to turn him northbound; I was unable to communicate with him because he was not on my low altitude frequency; thus he was continuing on an eastbound heading. I called sbn approach and pointed out the aircraft before he entered their airspace. He was point out approved with the sbn controller. I then advised C90 controller that aircraft Y was eastbound and NORDO. They acknowledged. I made several attempts during this time to contract both aircraft; both though back up frequencies; and also by having other aircraft relay. I'm not sure which was successful; but both aircraft were successfully placed on the right frequency with C90. Although this is a clear case of me failing to change the aircraft to the correct frequency; it is an issue that has potential to occur frequently; especially when the airspace is very busy. If an aircraft is NORDO in the in-flight stage; there are normally very few issues; however; when an aircraft is entering a very busy approach control; such as C90; it is a very bad location to have a NORDO aircraft. I think that with the size of the airspace; there is the possibility to have 'one' good frequency that covers the entire airspace so that this is not an issue at all. My recommendation would be to do just that and have one frequency for the airspace; again; especially since a large part of the procedures in the airspace involve sequencing C90 metropolitan arrivals.

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Original NASA ASRS Text

Title: ZAU Controller described an airspace incursion event when two aircraft with similar call signs failed to acknowledge instructions; the event complicated because of limited radio coverage.

Narrative: Aircraft X; a LJ35; was on course to BEARZ intersection for PWK. When I issued a descent to 4;000 FT for Aircraft X; I failed to change his frequency to my low altitude frequency; which led to complications later. Aircraft Y; a C550; was also on course for PWK over BVT then BEARZ intersection. Aircraft Y was much slower than Aircraft X and thus the plan was to turn Aircraft Y east until he was far enough behind Aircraft X for required spacing; and then turn him to BEARZ. I also failed to put Aircraft Y on my low altitude frequency when I issued a descent to 4;000 FT. Aircraft X cut through SBN Approach airspace on his way to BEARZ; thus; he was pointed out to the SBN Controller descending towards BEARZ. As the aircraft approached my boundary with C90; it was time to turn Aircraft Y to a 090 heading so he would fall behind Aircraft X; however; when I issued the clearance; I inadvertently used the abbreviated call sign [for] Aircraft X instead of Aircraft Y. Because the aircraft was not properly placed on my low altitude frequency; the pilot heard my clearance and took it; but I was unable to hear his communication back to me when he read back the clearance. Thus; Aircraft X took the clearance and turned eastbound further into SBN Approach airspace at 4;000 FT. I called SBN Controller and advised them of the situation and they advised that the aircraft was 'still point out approved.' I then turned Aircraft Y to a 090 heading and called C90 to work out a plan. They advised me to put Aircraft Y on a north heading and that he was RADAR contact. When I tried to contact Aircraft Y to turn him northbound; I was unable to communicate with him because he was not on my low altitude frequency; thus he was continuing on an eastbound heading. I called SBN Approach and pointed out the aircraft before he entered their airspace. He was point out approved with the SBN Controller. I then advised C90 Controller that Aircraft Y was eastbound and NORDO. They acknowledged. I made several attempts during this time to contract both aircraft; both though back up frequencies; and also by having other aircraft relay. I'm not sure which was successful; but both aircraft were successfully placed on the right frequency with C90. Although this is a clear case of me failing to change the aircraft to the correct frequency; it is an issue that has potential to occur frequently; especially when the airspace is very busy. If an aircraft is NORDO in the in-flight stage; there are normally very few issues; however; when an aircraft is entering a very busy Approach Control; such as C90; it is a very bad location to have a NORDO aircraft. I think that with the size of the airspace; there is the possibility to have 'one' good frequency that covers the entire airspace so that this is not an issue at all. My recommendation would be to do just that and have one frequency for the airspace; again; especially since a large part of the procedures in the airspace involve sequencing C90 metropolitan arrivals.

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.