LR35 CARGO FLT CLRED TO CROSS MUGZY 6000 FT. DME WAS GIVING PROBS AND CAPT RETUNED AND FOUND ONLY 18 DME FROM STW. CAPT TOOK THE ACFT AND EXPEDITED THE DSCNT. MOMENTARILY LOST COM WITH CTLR. WHEN COM MADE CTLR SAID 5 E OF MUGZY AND ONLY CLRED TO 6000 FT. HAD DSNDED TO 5000 FT. RETURNED TO 6000 FT AND CONTINUED THE APCH TO TEB.

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WE WERE GIVEN DSCNT TO CROSS MUGZY INTXN AT 6000 FT (COPLT WAS FLYING). SHORTLY AFTER; THE CTLR STATED WE WERE TO HOLD AT MUGZY AS PUBLISHED; 6000 FT. BEFORE OUR DSCNT THE CTLR ASKED IF WE WERE GOING TO MAKE MUGZY AT 6000 FT; AND WE SAID YES. ASSUMING THERE WAS SOMETHING THAT DIDN'T LOOK RIGHT TO THE CTLR WE STARTED DOWN OUT OF FL190. WE THEN STARTED TO CHK OUR NAV INFO AND DISCOVERED THAT WE WERE MUCH CLOSER TO MUGZY THAN WE THOUGHT (APPROX 18 DME). I THEN TOOK CTL OF THE AIRPLANE AND MADE A RAPID DSCNT TO CROSS MUGZY AT 6000 FT. IN THE DSCNT WE EXPERIENCED A MOMENTARY NAV/COM FAILURE. WE DISCOVERED THE COM FAILURE WHEN WE HEARD ATC YELLING AT US. IN ALL OF THE CONFUSION WE PASSED THE HOLDING FIX AND EVIDENTLY WENT TO APPROX 5500 FT. WE THEN ASKED ATC FOR HELP IN CORRECTING OUR COURSE. WE GOT BACK ON COURSE AND DID NOT EXPERIENCE FURTHER DIFFICULTIES. I THINK CLOSER XCHKING OF NAV INFO WILL HELP IN THE FUTURE. I ALSO THINK THAT IF ATC SEES SOMETHING THAT DOESN'T LOOK LIKE A GOOD SIT OCCURRING (SUCH AS WHAT WE HAD EXPERIENCED) THEY SHOULD INCLUDE IN THEIR COMMENTS SOMETHING TO HELP VERIFY THE AIRPLANE'S DISTANCE AND ALT AND NOT JUST; ARE YOU GOING TO MAKE IT DOWN. SUPPLEMENTAL INFO FROM ACN 354669: I ADVISED THE CAPT THAT THE DME DID NOT APPEAR TO BE CORRECT. HE IMMEDIATELY RECYCLED THE DME WHICH NOW READ 18 MI TO STW.