SMA EXPERIENCES INTERMITTENT DME INDICATIONS ON LOC DME APCH.

Narrative

I WAS TRACKING THE LOC OF HAYWARD ARPT'S LOC DME 28L APCH AT 6000 FT MSL ABOUT 18 MI OUT. BAY APCH TOLD ME TO CROSS 'BRIEN' (11.9 DME) AT OR ABOVE 4000 FT MSL AND CLRED ME FOR THE APCH. AS I WAS DSNDING; AT ABOUT 14-15 DME OUT; THE DME INDICATION WENT OUT. I RECHKED ALL OF MY AVIONICS TO SEE IF THE PROBLEM WAS WITH MY ACFT. EVERYTHING SEEMED SET UP CORRECTLY. THE DME INDICATION CAME BACK ON AT ABOUT 11.0 DME AND I NOTICED I HAD ALREADY DSNDED THROUGH 4000 FT MSL. IN BEING DISTRACTED BY THE PROBLEMATIC DME INDICATIONS; I MAY HAVE DSNDED SLIGHTLY BELOW 4000 FT MSL BEFORE 'BRIEN' (11.9 DME). I ADVISED BAY OF MY PREVIOUS DME PROBLEMS AND WAS THEN CLRED TO HAYWARD TWR FREQ. AS I CONTINUED ON THE APCH THE DME WENT OUT AGAIN FOR A SHORT PERIOD OF TIME. I AGAIN ADVISED TWR OF THE SITUATION. I CHKED MY DME AFTER LNDG AT HAYWARD'S GND CHK POINT AND IT WORKED CORRECTLY. IN THE PAST I HAVE HAD SIMILAR SITUATIONS WITH THE DME ON THIS APCH. FURTHERMORE; I HAVE HAD DISCUSSIONS WITH OTHER PLTS IN OTHER ACFT WHO HAVE EXPERIENCED THE SAME SITUATION. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES HIS DME IN ACFT HAS BEEN CHKED WITH NO PROBLEM FOUND. HWD EQUIP ON THIS DME APCH HAS GONE DOWN FOR MAINT A COUPLE OF TIMES. AT ABOUT 12 DME THE SIGNAL GOES OFF AND ON; THEN AT 7 MI SEEMS TO BE A STRONG INDICATION AGAIN. HE WAS DSNDING THROUGH ACTUAL IFR AND NIGHT TIME WHEN THIS OCCURRED. RPTR QUITE UPSET DUE TO HIGH TERRAIN AT THIS AREA OF THE APCH. SINCE HE IS NOT THE ONLY PLT WHO HAS EXPERIENCED THIS; HE FEELS IT SHOULD BE CHKED.