A DSNDING FALCON 50 FAILS TO CROSS THE 40 DME SW OF ATL AT 14000 FT AND 250 KTS WHEN THE CREW REALIZES; TOO LATE; THAT THEIR DME EQUIP WAS PROVIDING ERRONEOUS INFO.

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ON A DSCNT VECTOR OUT OF FL240; 90 DME SW OF ATL; WE WERE CLRED TO CROSS 40 DME SW ATL AT 12000 FT AT 250 KTS. I WAS NAVING/FLYING WITH THE AUTOPLT ENGAGED IN FMS MODE BACKED UP WITH #2 VOR SELECTED TO ATL (FREQ 116.9); GND SPD APPROX 400 KTS (50 MI SW OF XING POINT.) WE CALCULATED APPROX 7 MINS TO LOSE 12000 FT AND TO SLOW TO 250 KTS -- WELL WITHIN THE PARAMETERS OF A SMOOTH; COMFORTABLE DSCNT PROFILE (APPROX 1800 FPM RATE OF DSCNT). I ELECTED TO INITIALLY DSND AT 2500 FPM TO ALLOW AMPLE TIME TO REACH THE XING RESTR POINT AND TO SLOW TO THE 250 KT XING SPD LIMIT. SHORTLY AFTER INITIATING THE DSCNT; IN THE MIDST OF COMPLETING THE DSCNT CHKLIST; THE CTLR ASKED IF WE WERE GOING TO BE ABLE TO MAKE THE XING RESTR. THE PNF REPLIED; 'NO PROB' AFTER WHICH WE BOTH NOTED A DISCREPANCY OF APPROX 10 NM BTWN FMS AND VOR DME READOUT. WHILE CONTINUING THE DSCNT; WE OBSERVED THE DME DISTANCES DECREASE; BOTH FMS AND VOR DME READOUTS (CLOSURE RATES) RAPIDLY INCREASED UNTIL APPROX 20 DME WHEN ALMOST INSTANTANEOUS EQUALIZATION OF VOR AND FMX DME MILEAGE INDICATIONS SHOWED US TO BE WITHIN 3 DME OF OUR XING RESTR AND STILL AT APPROX 15000 FT AT APPROX 280 KTS. FREQ CONGESTION DUE TO HIGH/HVY CTLR WORKLOAD MADE IT IMPOSSIBLE TO NOTIFY THE CTLR OF OUR INABILITY TO MEET OUR XING RESTR OF 12000 FT AT 250 KTS. I IMMEDIATELY DEPLOYED FULL AIR BRAKES AND WE REACHED OUR XING POINT AT 14000 FT (+2000 FT) AT 280 KTS (+30 KTS). WE SUBSEQUENTLY LEVELED AT 12000 FT AT 250 KTS; APPROX 3.5 MI (DME) SW ATL (-5 DME FROM CLRED XING POINT). WHEN ADVISED TO CHANGE TO NEXT CTLR; PNF DID NOT INFORM CTLR OF DEV FROM XING RESTR BECAUSE OF CTLR WORKLOAD AND FREQ CONGESTION. WE CONTINUED TO DEST (ATL) WITHOUT FURTHER INCIDENT AND WERE NEVER QUERIED BY ANY SUBSEQUENT CTLR ABOUT OUR XING DEV. ON OUR NEXT LEG (ATL-TEB) ABOUT 4 HRS LATER; WE NOTICED AND EXPERIENCED A SIMILAR PROB ON VORTAC FREQ 113.0. MANUFACTURER HAS RECENTLY ISSUED SEVERAL VARIOUS ADVISORIES CONCERNING PROBS WITH THEIR UPDATED FMS UNITS -- ONE OF WHICH WAS RECENTLY INSTALLED IN THE ACFT WE WERE OPERATING AT THE TIME OF THE ABOVE RPTED INCIDENT. WE ARE CURRENTLY DISCUSSING THIS RECENT EVENT/PROB WITH MANUFACTURER'S TECHNICAL REPRESENTATIVES. SUPPLEMENTAL INFO FROM ACN 416123: DURING DSCNT (FO WAS FLYING) ATC GAVE A XING RESTR OF 14000 FT; 50 MI FROM ATL. COPLT WAS PRIMARILY USING #2 VOR DME INDICATIONS AND NOT THE FMS. ON SUBSEQUENT LEGS THE #2 VOR DME GAVE ERRONEOUS DME INDICATIONS AND WAS WRITTEN UP IN MAINT LOG. ALSO; #2 VOR FAIL INDICATION APPEARED ON FMS #1 ON THE NEXT LEG. I BELIEVE THE ERRONEOUS DME INDICATION COUPLED WITH ERRONEOUS FMS ETE'S (WHICH IS A SOFTWARE PROB ACKNOWLEDGED BY MANUFACTURER) LED TO THE XING ERROR. ATC ASKED US IF WE WERE GOING TO MAKE THE XING ALT AND I ASKED THE FO IF IT LOOKED GOOD; AND HE ACKNOWLEDGED WE WOULD. AT ABOUT 50 MI OUT OF ATLANTA; I QUESTIONED THE FO THAT THE 2 VORS APPEARED NOT TO AGREE. WE WERE AT APPROX FL180 DSNDING. WE WERE THEN SWITCHED TO THE NEXT CTLR AND ASKED TO DSND TO 12000 FT. NOTHING ELSE WAS SAID. AS CAPT; I SHOULD HAVE MONITORED MORE CLOSELY THE INDICATIONS BUT WAS BUSY OUT OF MY SEAT OPENING THE MAIN DOOR CURTAIN AND ONCE BACK IN MY SEAT WAS TALKING WITH OPS ON THE GND.