AN SMA TWIN PLT HAD A TEMPORARY RADIO FAILURE WHILE IN IMC ON AN IFR FLT PLAN.

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DULLES APCH CLRED NXXXX DIRECT FDK (APPROX 10-15 NM OUT) DSND TO 4000 FT AND CONTACT BWI APCH 126.75. ENRTE TO FDK; WE ATTEMPTED TO CONTACT BWI APCH APPROX 8-10 TIMES; USING BOTH #1 AND #2 COMS; HEADSET MIKE AND HANDHELD MIKE WITH BOTH SPEAKER AND HEADSET. UNABLE TO CONTACT. LOSS OF COM ON IFR FLT! WE HAD RECEIVED AWOS FOR FDK APPROX 35 NM OUT. OUR ETA OK; THEREFORE AT FDK VOR WE ELECTED TO START THE OUTBOUND LEG FOR ILS RWY 23 AT FDK. WE WERE OUTBOUND AND AT 3500 FT WHEN RADIO CONTACT WAS FINALLY ESTABLISHED WITH BALTIMORE. CONDITIONS WERE SCATTERED TO BROKEN. BALTIMORE ASKED IF WE HAD CANCELED OUR IFR FLT PLAN. WE ADVISED NEGATIVE; WE'RE STARTING APCH TO FDK MUNICIPAL. ATC ADVISED THERE WAS IFR TFC CLRED 3000 AND EBOUND. WE INITIATED AN IMMEDIATE CLB (1500 FPM RATE) BACK TO 4000 AND ASKED BALTIMORE IF THEY WANTED US TO RETURN TO THE VOR. ATC RESPONDED 'YES.' BACK ENRTE TO THE VOR; SCATTERED CONDITIONS DEVELOPED. WE REQUESTED CANCELLATION OF OUR IFR FLT PLAN AND RECEIVED SAME. ATC REQUESTED WE CALL SUPVR ON THE GND. WE CALLED AND TALKED TO SUPVR. WE ADVISED WE HAD LOST RADIO CONTACT WITH BALTIMORE APCH. ALL PERSONAL DATA WAS FURNISHED AT APPROX XAAM SEP/SAT/93. ON OUR RETURN FLT; WE ALSO HAD DIFFICULTY ESTABLISHING RADIO CONTACT WITH BALTIMORE APCH. TRIED 5-6 TIMES PRIOR TO ESTABLISHING CONTACT. HDG 090 DEGS AND 3000 FT ALT. SMT Y DEPARTED FDK APPROX 15-20 MINS PRIOR TO SMT X AND RPTED THEY ALSO ENCOUNTERED DIFFICULTY ESTABLISHING RADIO CONTACT WITH BALTIMORE 126.75. IT APPEARS THERE MAY BE A 'DEAD AREA' FOR RADIO COM IN THE BWI APCH SECTOR. SUGGEST THIS BE REVIEWED. ALSO; HAVE DULLES APCH ALERT ACFT OF POTENTIAL PROB WITH COM PRIOR TO HDOF. DULLES APPEARS TO BE GEOGRAPHICALLY CLOSER TO FDK. PERHAPS THEY SHOULD HANDLE THE APCH TO FDK MUNICIPAL? CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTING PLT STATES THAT HE WAS 'IN AND OUT' OF IMC AT THE TIME OF THE RADIO FAILURE. HE WAS OUT OF RADIO CONTACT ABOUT 8 MINS. HE DID NOT SQUAWK 7600; AND CANNOT FIND THIS REQUIREMENT IN FAR 91. THE RPTR COULD NOT FIND ANYTHING WRONG WITH HIS RADIOS WHILE ON THE GND AT FDK. THE FAA HAS CONTACTED HIM BUT HAS MADE NO THREATENING MOVEMENTS TOWARDS HIS CERTIFICATE.