C501 CREW HAD VHF RADIO PROBS WHILE DSNDING TO AN ARPT WITHIN DC ADIZ.

Narrative

ON THE ABOVE DATE THE ACFT EXPERIENCED A GRADUAL LOSS OF COM EFFECTIVENESS. WHILE WE WERE ABLE TO HEAR THE CTR AND APCH TO SOME EXTENT; ATC WAS NOT ABLE TO HEAR US CONSISTENTLY. WE WERE ON THE COATT ARR INTO THE DC METROPLEX FOR A LNDG AT HEF. WE WERE LEVEL AT FL200 WHEN THE FAILURE OCCURRED. OUR LAST RELIABLE RECEIVED XMISSION WAS TO CROSS FALKO INTXN AT 10000 FT AND 250 KTS. UPON ARR AT FALKO AND BEING UNABLE TO COMMUNICATE WITH ATC WE DECLARED AN EMER BY BROADCASTING IN THE BLIND ON 121.5 AND SQUAWKING 7700 FOR 1 MIN AND THEN CHANGING TO 7600. WE BROADCAST OUR INTENTION TO DSND WBOUND AND REMAIN VFR AND REMAIN CLR OF THE ADIZ. AT THIS TIME WE RECEIVED A XMISSION TO CONTACT PCT TRACON ON 124.65. WE WERE ABLE TO COMMUNICATE ON A LIMITED BASIS. WE ADVISED THEM WE WERE GOING TO DIVERT TO W66. THE CAPT THEN SPECIFICALLY REQUESTED THAT ATC ADVISE US IF THEY WOULD ALLOW US TO LAND AT OUR ORIGINAL DEST OF HEF; AS THERE WERE FACILITIES THERE FOR THE REPAIR OF THE ACFT. PLUS THAT WAS WHERE THE PAX WANTED TO LAND ANYWAY. THE CAPT SPECIFICALLY REQUESTED THAT ATC ALLOW THE EMER ACFT TO LAND AT HEF. ATC GAVE US PERMISSION TO ENTER THE ADIZ AS AN EMER ACFT. WE THEN LANDED WITHOUT INCIDENT.