A DA20 LANDS AT LAREDO ARPT WITHOUT OBTAINING OR NOTING A LNDG CLRNC WHEN THEIR RADIO IS UNABLE TO RECEIVE GND-TO-AIR.

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ON SEP/XA/99; I WAS THE FO ON A FLT FROM SALTILLO; MEXICO; TO LAREDO; TX. THE FLT DEPARTED SALTILLO AT APPROX PM15Z. THE FLT WENT WITH RELATIVELY NO PROBS WHILE IN THE MEXICAN AIRSPACE. HOWEVER; WHILE DSNDING INTO LAREDO; WHEN MEXICO'S ATC GAVE US A FREQ CHANGE TO ZHU WE BEGAN TO HAVE RADIO PROBS. THE CAPT ATTEMPTED TO CONTACT ZHU ON THE ASSIGNED FREQ; BUT IT APPEARED TO HAVE A STUCK MIKE. AS THE CAPT TRIED DIFFERENT METHODS TO CONTACT ZHU; I CONTINUED ON OUR FLT PLAN RTE; WHICH WAS NEWLA VOR (NLD) DIRECT TO LAREDO VOR (LRD). WHILE PROCEEDING DIRECTLY TO LAREDO VOR; THE RADIOS BEGAN TO WORK AND THE CAPT ESTABLISHED RADIO CONTACT WITH ZHU. TO COMPLICATE MATTERS; MEXICO'S ATC DID NOT PASS ON ANY FLT INFO TO ZHU WITH THE HDOF. SO; ZHU TOLD US TO MAKE AN IMMEDIATE L TURN TO A 300 DEG HDG AND INFORMED US THAT WE WERE THE ONES WITH A STUCK MIKE. ZHU GATHERED OUR INFO ON OUR FLT PLAN FROM US AND PROCEEDED TO GIVE US VECTORS FOR A VISUAL APCH INTO LAREDO. WE WERE VECTORED UNTIL ESTABLISHED ON APPROX A 5 MI FINAL WHEN WE WERE CLRED FOR A VISUAL APCH TO RWY 17L AT LAREDO. THE RADIOS WORKED FINE ONCE RADIO CONTACT WAS ESTABLISHED WITH ZHU UP TO THE POINT WHEN WE WERE TOLD TO CONTACT THE TWR. WHEN THE CAPT SWITCHED TO THE TWR FREQ; WE COULD HEAR THE SAME STATIC NOISE THAT WE THOUGHT EARLIER WAS A STUCK MIKE. WE WERE UNABLE TO RECEIVE OR XMIT TO LAREDO TWR. I SLOWED THE ACFT TO FINAL APCH SPD WHILE THE CAPT ATTEMPTED TO CONTACT THE TWR. THE CAPT TRIED THE PREVIOUS FREQ; CHKED THE CIRCUIT BREAKERS; UNPLUGGED THE MIKES INDEPENDENTLY; CHKED THE PUSH-TO-TALK BUTTONS AND AUDIO PANELS; ETC; WITH NO PREVAIL. WE WERE STILL UNABLE TO COMMUNICATE WITH THE TWR. WE HAD SQUAWKED 7600 ON THE XPONDER; AND AT THIS POINT WERE APCHING SHORT FINAL. I TOLD THE CAPT THAT I THOUGHT WE SHOULD DO A GAR SINCE I COULD NOT SEE A STEADY GREEN LIGHT GUN SIGNAL FROM THE TWR. THE CAPT STATED NO; THAT WE WERE GOING TO LAND NOW BECAUSE IT WOULD BE SAFER THAN GOING AROUND. WHEN WE WERE IN RADIO CONTACT; WE HAD BEEN GIVEN TA'S OF OTHER ACFT IN THE AREA. I AM NOT SURE IF THE CAPT SAW A STEADY GREEN LIGHT FROM THE TWR; BUT WE WENT AHEAD AND LANDED THE ACFT ON RWY 17L. THE CAPT TAXIED THE ACFT OFF THE RWY AND WENT TO GET HIS HAND-HELD TRANSCEIVER OUT OF HIS FLT BAG. I COULD SEE THAT THE TWR WAS GIVING US A FLASHING GREEN LIGHT TO TAXI. I INFORMED THE CAPT THAT I COULD SEE THE LIGHT SIGNAL AND MOMENTS LATER THE CAPT HAD HIS HAND-HELD AND CALLED THE TWR WITH IT. THE TWR GAVE US TAXI INSTRUCTIONS TO CUSTOMS AND ASKED US TO CALL THEM ON THE TELEPHONE. AS I WAITED FOR OUR PAPERWORK AT UNITED STATES CUSTOMS; THE CAPT CALLED THE TWR ON THE TELEPHONE. I DO NOT KNOW THE DETAILS OF THE CAPT'S CONVERSATION WITH THE TWR; BUT THE CAPT TOLD ME AFTERWARDS THAT THE PERSON IN THE TWR JUST WANTED TO KNOW THE NATURE OF OUR PROB. THE CAPT ALSO STATED THAT THE TWR SAID THEY WERE GIVING US A STEADY GREEN LIGHT TO LAND AND THAT THE TWR SAID THEY DID NOT WANT US TO DO A GAR.