PLT OF A BE55 EXPERIENCED A LOSS OF COM WHILE DEPARTING PWK ON AN IFR FLT PLAN. THE MIKE JACK RECEPTACLE FELL OFF THE PEDESTAL INTERIOR; DISCONNECTING THE MIKE JACK; WHICH PREVENTED VOICE MODULATION. THE RPTR WAS UNABLE TO RETRIEVE THE RECEPTACLE WHILE FLYING; SO HE TURNED BACK TOWARD A NON TWR ARPT AND THEREBY RECEIVED ATC ATTN AND VECTORS THROUGH CARRIER WAVE XMISSION ACKNOWLEDGMENT.

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I DEPARTED PALWAUKEE ARPT ON AN IFR FLT PLAN. WHEN THE PALWAUKEE TWR CTLR HANDED ME OFF TO CHICAGO DEP; I FOUND I COULD NOT TALK TO THE NEW CTLR. BRIEF EXPERIMENTATION REVEALED THAT I COULD HEAR INCOMING XMISSION; AND THAT I COULD SEND OUT CARRIER WAVE XMISSIONS; BUT I COULD NOT MAKE MY VOICE HEARD. MY 1976 BEECHCRAFT BARON B55 HAS THE MIKE JACK RECEPTACLE MOUNTED VERTLY INSIDE A PEDESTAL BTWN THE FRONT SEATS. EXAMINATION SHOWED THAT THE MIKE JACK RECEPTACLE RETAINING NUT HAD WORKED ITSELF OFF THE RECEPTACLE; ALLOWING THE RECEPTACLE TO FALL DOWN INTO THE PEDESTAL INTERIOR AND DISCONNECTING THE MIKE JACK. I COULD NOT MANUALLY RETRIEVE THE JACK RECEPTACLE WHILE FLYING THE AIRPLANE. THE CHICAGO DEP CTLR FOUND THAT SHE COULD COMMUNICATE WITH ME BY HAVING ME SQUAWK IDENT ON MY XPONDER TO ACKNOWLEDGE HER INSTRUCTIONS. SHE THEN DISCOVERED THAT SHE COULD MORE QUICKLY OBTAIN MY ACKNOWLEDGMENT OF HER XMISSIONS BY HAVING ME DEPRESS MY PUSH-TO-TALK MIKE SWITCH TWICE IN RAPID SUCCESSION. USING THIS METHOD; SHE TURNED ME AROUND TO RETURN AND INTERCEPT THE PALWAUKEE ILS. SHE HANDED ME OFF TO THE TWR; AND I LANDED AND TAXIED BACK TO MY HANGAR UNEVENTFULLY. I HAVE HAD MY ACFT REPAIRED AND I SUGGEST ALL BARONS; AND ALL OTHER ACFT HAVING THESE JACK PLUG RECEPTACLES; WHICH ARE VERTLY MOUNTED INSIDE A PEDESTAL; BE CHKED TO BE SURE THAT THE RECEPTACLES ARE SECURELY MOUNTED BELOW THE PEDESTAL TOPS; AND THAT THE RETAINING NUTS ARE TIGHTENED. THESE RETAINING NUTS SHOULD BE REPLACED WITH LOCK NUTS OR LOCK WASHERS AND NUTS TO INSURE THAT THE MIKE PLUG JACKS DO NOT WORK LOOSE AND SEPARATE FROM THE MIKE PLUGS INFLT. THE ADJACENT HEADPHONE JACK PLUG RECEPTACLES SHOULD ALSO BE CHKED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THIS RPTR HAS SINCE REVIEWED PLT'S TECHNICAL MANUAL AND HAS FOUND NO NEW SOLUTION FOR THIS SIT OTHER THAN PREVENTIVE MAINT. RPTR WILL PASS ALONG HIS EXPERIENCE TO THE LCL DEALER FBO -- SO OTHER BARONS MIGHT BE CHKED.