Narrative:

This situation was scary but in a way controled at all times. Aircraft #1 was climbing wbound from columbus, oh. Aircraft #1 was assigned FL230. Aircraft #1 responded to clearance. Aircraft #1 was handed off and switched to my frequency. Aircraft #1 microphone quit functioning. Response to frequency change not heard on previous frequency. Previous controller tried to switch aircraft #1 several more times. Previous controller called me and asked was I talking to aircraft. Thinking aircraft might be sitting on my frequency but not checked on, I climb aircraft #1 to FL280. I get no response. I assume aircraft #1 still cleared to FL230. I notice aircraft #1 leaving FL245 so I start calling his call sign -- no response. Not knowing how high aircraft #1 is going, I turn aircraft #2 from about 190 degree heading to 070 degree heading. Aircraft #2 much slower and having trouble getting out of aircraft #1's way. Commotion on frequency causes aircraft #1 to realize that I don't have control of events. Using a different microphone, we re-establish communications. He assures me he is only going to FL280. Positive separation? Pilot also makes reference to having problems with microphone in past. I should not check for aircraft by issuing clearance that requires readback. If pilot knows equipment may need maintenance, pilot shouldn't use it.

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Original NASA ASRS Text

Title: ZID CTLR EXPERIENCED POTENTIAL SEPARATION LOSS DURING ACFT COM PROB.

Narrative: THIS SIT WAS SCARY BUT IN A WAY CTLED AT ALL TIMES. ACFT #1 WAS CLBING WBOUND FROM COLUMBUS, OH. ACFT #1 WAS ASSIGNED FL230. ACFT #1 RESPONDED TO CLRNC. ACFT #1 WAS HANDED OFF AND SWITCHED TO MY FREQ. ACFT #1 MIKE QUIT FUNCTIONING. RESPONSE TO FREQ CHANGE NOT HEARD ON PREVIOUS FREQ. PREVIOUS CTLR TRIED TO SWITCH ACFT #1 SEVERAL MORE TIMES. PREVIOUS CTLR CALLED ME AND ASKED WAS I TALKING TO ACFT. THINKING ACFT MIGHT BE SITTING ON MY FREQ BUT NOT CHKED ON, I CLB ACFT #1 TO FL280. I GET NO RESPONSE. I ASSUME ACFT #1 STILL CLRED TO FL230. I NOTICE ACFT #1 LEAVING FL245 SO I START CALLING HIS CALL SIGN -- NO RESPONSE. NOT KNOWING HOW HIGH ACFT #1 IS GOING, I TURN ACFT #2 FROM ABOUT 190 DEG HDG TO 070 DEG HDG. ACFT #2 MUCH SLOWER AND HAVING TROUBLE GETTING OUT OF ACFT #1'S WAY. COMMOTION ON FREQ CAUSES ACFT #1 TO REALIZE THAT I DON'T HAVE CTL OF EVENTS. USING A DIFFERENT MIKE, WE RE-ESTABLISH COMS. HE ASSURES ME HE IS ONLY GOING TO FL280. POSITIVE SEPARATION? PLT ALSO MAKES REF TO HAVING PROBS WITH MIKE IN PAST. I SHOULD NOT CHK FOR ACFT BY ISSUING CLRNC THAT REQUIRES READBACK. IF PLT KNOWS EQUIP MAY NEED MAINT, PLT SHOULDN'T USE IT.

Data retrieved from NASA's ASRS site as of July 2007 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.