B737-300 FLC ON THE MT VERNON VISUAL TO DCA SUFFERS A TEMPORARY LOSS OF COM FREQ WHEN THEY ARE UNABLE TO CONTACT APCH CTLR ON TWO SEPARATE FREQS. PIC FINALLY SWITCHES TO TWR FOR VISUAL APCH CLRNC.

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WE WERE TALKING TO THE FINAL APCH CTLR (DCA APCH CTL). WE WERE GIVEN A 250 DEG HDG AND A DSCNT TO 2000 FT. WE WERE APPROX 7 MI SE OF DCA. AFTER APPROX 30 SECONDS OF NOT HEARING THE CTLR; WE QUERIED HIM. THERE WAS NO RESPONSE AND WE COULD NOT HEAR ANYONE ELSE TALKING ON THE FREQ. WE TRIED TO RAISE HIM SEVERAL MORE TIMES; BUT TO NO AVAIL. WE SWITCHED TO ANOTHER FREQ (124.7). WE COULD HEAR COM ON THIS FREQ; BUT THEY COULD NOT HEAR US. WE OBSERVED ANOTHER AIRPLANE APCHING FROM THE S (LNDG RWY 36). WE LEVELED OFF AT 3500 FT TO AVOID A POTENTIAL CONFLICT. WE WERE OVER THE POTOMAC AT THIS TIME AND HAD BEEN TOLD EARLIER TO EXPECT THE MT VERNON VISUAL. WE DECIDED TO TURN N TOWARD THE ARPT AND SWITCH TO TWR. WE ALSO NOTICED THE OTHER ACFT BREAKING OFF TO THE W. WE WERE ABLE TO TALK TO THE TWR AND WERE INSTRUCTED TO FLY UP THE RIVER FOR RWY 36. WE WERE CLRED TO LAND; WHICH WE DID. AFTER LNDG GND CTL ASKED US TO CALL THE TRACON SUPVR. I CALLED HIM ONCE INSIDE. HE SIMPLY WANTED TO KNOW WHAT HAPPENED. I DESCRIBED TO HIM EVERYTHING AS STATED ABOVE. HE SAID HE DID NOT HAVE A PROB WITH WHAT WE DID AND THAT WE DID EXACTLY WHAT HE WOULD HAVE EXPECTED US TO DO IN THIS SIT. I ASKED HIM IF THEY HAD EXPERIENCED LOSS OF COM PROBS IN THAT AREA AND HE STATED THAT THIS WAS THE FIRST IN A WHILE.