C90 Controller described a loss of separation event resulting from a 'stuck microphone' issue.
Synopsis
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.
Second reporter narrative
Inbound to MDW for ILS 31C; circle 22L; given vector to intercept LOC at 4;000 FT MSL. About 15 miles out; we received a TA for traffic at co-altitude about five miles ahead. Found traffic visually turning away. No RA. Commented; to the First Officer; that ATC should have given us a heads up. Then; realized the radio had been quiet for the last couple of minutes and we should have been given a descent. Keyed mic to query ATC and realized it was stuck. ATC said they were having a radio problem; and after landing; Ground told us we were the problem. Aircraft had been written up the day before for same problem. Sign off was OK for the adjusted switch operational checks. I was trying to be very careful with the switch but was not careful enough. Reaching gate; switch was working fine. We had an unscheduled aircraft swap on a through flight. Gave outbound crew a thorough brief on problem and suggested they consider calling Maintenance but did not write it up.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.