Narrative:

I am a cpc-it; certified on sector 1. I was vectoring aircraft to the ILS runway 31C approach; circling to runway 22L. I had several aircraft on frequency inbound for mdw; and at least one aircraft inbound to another airport in my airspace. A B737 was on the localizer and level at 5;000; where he would normally be at 4;000; due to an aircraft inbound to gyy at 4;000. A B350 was inbound from the west at 5;000; on a heading of 120 to position him behind another aircraft on the final. My intention was to descend him to 4;000 as I turned base leg due to other traffic inbound to gyy at 4;000; then clear the B737 after the B350 for the approach once I had the proper spacing. I attempted to turn the B350 to a heading of 050 and descend him to 4;000; but received no response. I issued instructions to several other aircraft but received no response. I switched to the stand by transmitter and received no response; and then used the ecs and received no response. I could hear a one-sided conversation in my headset; indicating a stuck mic by one of the aircraft on my frequency. The B350 had returned to his previous frequency; and the sector 2 controller turned the B350 away from the B737; but I was informed that a loss of separation had occurred. I believe it was determined that the B737 had the stuck mic. Ironically; I could hear the B737 mention how close the B350 was; and questioned the other pilot in his cockpit about whether that aircraft was supposed to be in front of them. Recommendation; had I left the B737 at 6;000 instead of descending him to 5;000; I would have had vertical separation; although he may have been high on the glide slope at that altitude. Training to mitigate stuck-mic issues for flight crews and controllers alike could help prevent the issue in the future.

Related reports:

Google
 

Original NASA ASRS Text

Title: C90 Controller described a loss of separation event resulting from a 'stuck microphone' issue.

Narrative: I am a CPC-IT; certified on Sector 1. I was vectoring aircraft to the ILS Runway 31C Approach; circling to Runway 22L. I had several aircraft on frequency inbound for MDW; and at least one aircraft inbound to another airport in my airspace. A B737 was on the localizer and level at 5;000; where he would normally be at 4;000; due to an aircraft inbound to GYY at 4;000. A B350 was inbound from the west at 5;000; on a heading of 120 to position him behind another aircraft on the final. My intention was to descend him to 4;000 as I turned base leg due to other traffic inbound to GYY at 4;000; then clear the B737 after the B350 for the approach once I had the proper spacing. I attempted to turn the B350 to a heading of 050 and descend him to 4;000; but received no response. I issued instructions to several other aircraft but received no response. I switched to the stand by transmitter and received no response; and then used the ECS and received no response. I could hear a one-sided conversation in my headset; indicating a stuck mic by one of the aircraft on my frequency. The B350 had returned to his previous frequency; and the Sector 2 Controller turned the B350 away from the B737; but I was informed that a loss of separation had occurred. I believe it was determined that the B737 had the stuck mic. Ironically; I could hear the B737 mention how close the B350 was; and questioned the other pilot in his cockpit about whether that aircraft was supposed to be in front of them. Recommendation; had I left the B737 at 6;000 instead of descending him to 5;000; I would have had vertical separation; although he may have been high on the glide slope at that altitude. Training to mitigate stuck-mic issues for flight crews and controllers alike could help prevent the issue in the future.

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.