ZKC CTLR DESCRIBED CTLR CONCERNS WHEN ACFT DESCENDING FROM FL400 LOST TRANSPONDER AND RADIOS FOR 15 MIN.

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I WAS WORKING 7 OR 8 ACFT FROM FL330 AND ABOVE. I NEEDED TO GET AN OMA ARR FLT DOWN SO I ISSUED A XING RESTR TO THE LR60; WHO IS MY OMA FLT. AS THE LR60 APCHED THE NEXT SECTOR; DSNDING TO FL340; SUDDENLY THE XPONDER DISAPPEARED FROM MY DISPLAY. I CALLED THE LR60 BUT GOT NO RESPONSE. I ASKED A NEARBY FLT IF THEY COULD HEAR THE LR60 CALLING ZKC AND GOT A NEGATIVE. I VECTORED 2 NEARBY AIRLINERS OVER THE LOCATION THAT THE LR60 DISAPPEARED TO LOOK FOR A GND FIRE BUT THEY HAD A BROKEN LAYER UNDERNEATH THEM AND COULD NOT SEE ANYTHING THAT LOOKED LIKE A DOWNED FLT. I AM WRITING TO NASA AVIATION SAFETY RPTING SYS BECAUSE OF WHAT HAPPENED THAT CAUSED AIR TFC TO THINK A CRASH HAD OCCURRED. THE FLT WAS IDENTED AND FOUND THE CORRECT CTR FREQ ABOUT 15 MINS AFTER LOSING ITS XPONDER AND WAS ON COURSE. WHEN THE PLT CALLED THE CTR AFTER LNDG; AS PER MY REQUEST; I WAS INFORMED THAT A SWITCH WAS INADVERTENTLY SWITCHED WHICH PUT THE XPONDER ON STAND-BY AND SENT THE RADIOS TO A DEFAULT COMPANY FREQ. SO THE PLT SPENT THE NEXT 15 MINS TRYING TO LOCATE THE CTR FREQ; WHILE ALSO PREPARING TO LAND AT OMA; PLUS FLY THE LR60. I WAS ABSOLUTELY SURE I HAD LOST THE LR60 AND MUCH EFFORT WAS SPENT ON BEHALF OF THE SYS TRYING TO DETERMINE WHAT HAPPENED. I WAS VERY GLAD THAT I HAD ISSUED A XING RESTR; BECAUSE THIS FLT WAS HEADING INTO A ZMP SECTOR THAT WAS BUSY AND THEY ONLY HAD TO PROTECT FL340. I AM NOT A PLT AND I DON'T KNOW THE SWITCH THAT THE PLT IS REFERRING TO; BUT I HOPE THIS WON'T HAPPEN AGAIN.