FLC OF AN MD88 FOUND APCH CTLR HAPPY TO HEAR FROM THEM AFTER CHANGING TO ANOTHER FREQ SINCE THEY HAD A STUCK MIKE; AND DID NOT KNOW IT; CAUSING THE CTLR TO BE BLOCKED IN COMMUNICATING WITH OTHER ACFT.

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DSCNT INTO ATL WE HAD AN AIR CONDITIONING/PRESSURIZATION 'FLOW' LIGHT ILLUMINATE. FO WAS FLYING THE ACFT AND HE WAS GIVEN THE JOB OF MONITORING THE RADIOS. I WENT TO THE POM TO REVIEW AND APPLY ANY PROCS. WE WERE AT 12000 FT AND HANDED OFF TO APCH CTL. FO CHKED IN WITH APCH CTL ABOUT THE TIME I FINISHED WITH THE PROCS. WE WERE DISCUSSING THE NECESSARY THINGS TO INCLUDE IN THE WRITE-UP; WHEN WE BOTH NOTICED THE L PACK PRESSURE WAS MUCH LOWER THAN THE R. SOMEWHERE IN ALL OF THIS WE BOTH BECAME AWARE THAT WE WERE APCHING ATL VOR AND HAD NOT BEEN GIVEN A TURN TO DOWNWIND BY CTR. AT THIS POINT WE TRIED CALLING CTR 2-3 TIMES AND THEN STARTED HUNTING FOR ANOTHER FREQ TO TALK WITH THEM. OUR RADIO WAS ON FREQ X AND THE APCH PLATE LISTS FREQ Y. WE ASSUMED THE RADIO HAD INADVERTENTLY BEEN CHANGED. WE WENT TO FREQ Y AND ESTABLISHED CONTACT WITH ATL AS WE WENT OVER TOP ATL VOR. LNDG WAS UNEVENTFUL. I WAS ASKED TO CALL APCH ON THE PHONE. ON THE PHONE APCH CTL EXPLAINED THAT FREQ X WAS A GOOD FREQ AND THAT WE HAD A STUCK MIKE WHICH HAD BLOCKED THE ENTIRE FREQ TO ALL ACFT. HE STATED THAT IT REALLY CAUSED A LOT OF PROBS AND THAT THEY WERE ABOUT TO START HOLDING WHEN WE FINALLY MADE CONTACT. I APOLOGIZED FOR THE PROB; EXPLAINING THAT WE HAD NOT EVEN RECOGNIZED THAT WE HAD A STUCK MIKE. AS THE FO AND I TALKED LATER ABOUT THE PROB; WE WERE STILL UNABLE TO IDENT WHICH MIKE WAS STUCK OPEN OR WHEN IT CLRED UP.