FLC OF AN MD88 FAILED TO BE WHERE THEY WERE SUPPOSED TO BE DUE TO A MALFUNCTIONING DME WHICH CAUSED THE FMS TO PROVIDE INACCURATE GUIDANCE.

Narrative

ACFT EXPERIENCED DME TUNING AND FMS TRACKING PROBS. DME WAS UNRELIABLE BEYOND 40 NM ON ANY STATIONS UNTIL WITHIN 30 NM ATL. HOWEVER; IT APPEARED THROUGH VARIOUS INST XCHKS THAT WE WERE ABLE TO MAINTAIN NAV TO ATL. AFTER RECEIVING CLRNC TO HOLD AT MACEY; WE PROCEEDED INBOUND; ON COURSE; NOTING POS COORDINATES COUNTDOWN TO MACEY'S; AND WITH WIND READOUTS STARTING TO INCREASE THROUGH 200 KTS. DME READOUTS CONTINUED TO BE ERRATIC; BUT FROM OUR LAST CHK WE APPEARED TO BE WITHIN 1 MI OF OUR PLANNED POS DME WISE. ATL DME WAS UNRELIABLE; BUT OVER DDF OUR DME MATCHED OUR POS. WITHIN 5 MI OF MACEY ON OUR MAP; ATC SAID WE WERE 3 MI INSIDE MACEY AND TO TURN R 360 DEGS EVIDENTLY THE ERRORS AND OR UNRELIABILITY OF DME TUNING EXTENDED INSIDE EVEN 40 NM; AND ALLOWED OUR DME POS TO DRIFT RAPIDLY WITH THE BIG WINDS. WE GOT SEVERAL POS READOUTS FROM ATC AND WHILE TURNING IN HOLDING AND AS WE GOT CLOSER TO ATL; DME TUNING RETURNED SLOWLY. OUR FMS UPDATED ITSELF EVENTUALLY; OUR DME AND TRACK WAS RE- ESTABLISHED; AND WE MADE AN UNEVENTFUL APCH AND LNDG IN ATL. SUSPECT DME TUNING AND FMS EQUIP AS AN ACFT MALFUNCTION TO BE THE CAUSE OF THIS SIT.