AN MD80 PILOT REPORTS FOLLOWING A FAULTY DOCKING GUIDANCE AND NEARLY HITTING GND EQUIPMENT.

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TAXIED IN TO LINE UP ON DGS AT GATE AT ZZZ. 'MD80' DISPLAYED PROPERLY; AND NORMAL GUIDANCE CUES SHOWN. TAXIED VERY SLOWLY IN AND AT ABOUT 35-40 FT; DGS SHOWED 'STOP' WITH RED LIGHTS; AND THEN 'WAIT' AND 'ID FAILED.' I STOPPED THE ACFT. A RAMP PERSON ATTEMPTED TO WAVE US IN BY HAND; BUT I DECLINED TO FOLLOW HIS GUIDANCE IN CASE THERE REALLY WAS A PROB AND THE DGS WAS TRYING TO WARN ME. NOTIFIED RAMP CTL. AFTER ABOUT 2-3 MINS; DGS DISPLAY SEEMED TO RESET; AND GAVE DIRECTIONAL GUIDANCE; AND WHAT SEEMED LIKE ACCURATE DISTANCE DISPLAY. BEGAN SLOWLY MOVING AGAIN. EVERYTHING SEEMED NORMAL UNTIL ABOUT 8 FT ON THE DISPLAY. SEVERAL CARGO DOOR LIGHTS CAME ON AND A GND MAN BANGED LOUDLY ON THE SIDE OF THE PLANE. THIS USUALLY IS AN INDICATION THAT GND PWR HAS BEEN HOOKED UP. I STILL HAD 5 OR 6 FT TO TAXI AND I THOUGHT THAT THEY SHOULD NOT BE OPENING DOORS AND HOOKING UP EXTERNAL PWR WHILE THE ACFT IS STILL MOVING. INSIDE ABOUT 10 FT REMAINING; I BELIEVE THAT THE CAPT IS; AND MUST BE; TOTALLY DEPENDENT ON THE GUIDANCE INFO BEING PRESENTED ON THE DGS DISPLAY. I CANNOT BE LOOKING AROUND AND DOUBLE-CHKING ANYTHING AT THAT POINT BECAUSE WE ARE SO CLOSE TO HAVING TO STOP. I CONTINUED TO TAXI VERY SLOWLY AND AT ABOUT 2 FT; I NOTICED A GND MAN WAVING RAPIDLY FOR ME TO STOP THE ACFT. I STOPPED WITH 1 FT REMAINING ON THE DGS DISPLAY. WHEN I LOOKED AROUND; I NOTICED THAT THE FRONT OF THE TUG WAS NO LONGER IN SIGHT BELOW THE NOSE; AND I WAS ABOUT 10 FT PAST THE JETBRIDGE. I AM ABSOLUTELY SURE THAT IF I HAD NOT NOTICED THE RAMP PERSON TRYING FRANTICALLY TO GET MY ATTN TO STOP; THAT I WOULD HAVE BEEN VERY LIKELY TO HAVE HIT THE TUG WITH THE NOSE OF THE ACFT. WHAT IF IT WAS AT NIGHT; OR THERE WERE NO RAMP PEOPLE PRESENT? IS THE CAPT RESPONSIBLE FOR ACFT DAMAGE IN THIS SITUATION? I FEEL TOTALLY VULNERABLE TO A SYS THAT IS CLEARLY NOT AS RELIABLE AS IT NEEDS TO BE; YET THE PLTS HAVE BEEN PUT ON NOTICE THAT FAILURE TO USE THE DGS CAN BE PUNISHABLE BY TERMINATION. WE WERE VERY LUCKY THAT THE TOWBAR WAS NOT IN FRONT OF THE TUG; BECAUSE I ABSOLUTELY WOULD HAVE HIT THAT. THEY HAD TO BACK THE TUG UP TO FIT THE TOWBAR BTWN THE TUG AND THE NOSE GEAR. WHEN I WENT DOWN TO INSPECT THE PLANE FOR ANY DAMAGE; THE RAMP PERSON WHO TRIED TO WAVE ME IN TOLD ME THAT THE PREVIOUS ACFT ON THAT GATE HAD THE SAME PROB; ONLY THAT CAPT FOLLOWED THE RAMP PERSON'S HAND SIGNALS TO PARKING. APPARENTLY NO ONE NOTIFIED ANYONE THAT THIS DGS HAD MALFUNCTIONED PREVIOUS TO MY ARR; AND THEREFORE WE WERE PUT INTO HARMS WAY UNWITTINGLY; EVEN THOUGH THE RAMPERS KNEW THAT THE SYS HAD HAD A PROB. I AM SHAKEN AT HOW CLOSE I BELIEVE I CAME TO DAMAGING AN ACFT TODAY; THROUGH NO FAULT OF MY OWN THAT I CAN DISCERN. I AM ALSO UNHAPPY THAT CARGO DOORS WERE OPENING AND THAT PEOPLE HAD HOOKED UP EXTERNAL PWR TO MY ACFT AND WERE BANGING ON THE SIDE WHILE I WAS IN SUCH A VULNERABLE AND IMPORTANT PART OF THE SELF DOCKING PROC. THERE ARE SO MANY CRITICAL SAFETY ISSUES INVOLVED IN THIS INCIDENT TODAY THAT I AM NOT SURE WHERE TO START. OUR MANUAL; AND EVERYTHING I HAVE READ ABOUT THE DGS PROGRAM SAYS THAT 'THE CAPT IS RESPONSIBLE FOR CLEARING THE RAMP PARKING AREA' AND THAT 'THE DGS DOES NOT GIVE CLRNC FROM ALL OBJECTS.' INSIDE 10 FT; I AM TOTALLY LOOKING UP AT THE DGS DISPLAY AND AM RELYING COMPLETELY ON THE DGS INFO FOR DIRECTIONAL GUIDANCE; AND TO KNOW WHEN TO STOP. THIS IS A HUGE LIABILITY PROB FOR THE PLTS WHO TAXI THESE ACFT WHEN THE DGS SYS CLEARLY HAS SYS PROBS; YET THE COMPANY AND THE FAA STILL DEMAND THAT THE ULTIMATE RESPONSIBILITY FOR OBSTACLE CLRNC REMAINS WITH THE CAPT.