FLC OF A WDB ACR ACFT STRUCK ANOTHER ACFT WHILE PARKING CAUSING DAMAGE TO THE TAIL OF THE OTHER ACFT.

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WE MADE THE 90 DEG R-HAND TURN FROM THE TXWY AND INTERCEPTED THE YELLOW LEAD-IN LINE TO THE GATE. ALL INDICATIONS WERE NORMAL. GREEN LIGHT AND PROPER WAND SIGNALS FROM THE WING WALKERS. APPROX 20 FT FROM THE STOP POINT; THE GREEN LIGHT WENT BLANK. THE CAPT STOPPED THE ACFT. I ATTEMPTED TO ESTABLISH GND COM BY OPENING MY CLEARVIEW WINDOW TO SEE WHY WE STOPPED PREMATURELY. I STUCK MY HEAD FAR ENOUGH OUT TO SEE THE WING TIP; AND AT THAT MOMENT; I COULD SEE THAT WE CAME IN CONTACT WITH THE TAIL OF A PARKED ACFT. WE REMAINED PARKED UNTIL A RAMP MGR INDICATED THAT THE AREA WAS CLR; WE AGREED THAT IT WAS SAFE TO CONTINUE; AND THE CAPT MOVED THE ACFT THE LAST FEW FT TO THE GATE. OUR ACFT WAS ON THE YELLOW LINE AND WAS CORRECTLY POSITIONED. THE OTHER ACFT WAS NOT PARKED CORRECTLY; ITS NOSE GEAR WAS NOT ON ITS CTRLINE AND WAS PARKED APPROX 10 FT SHORT OF WHERE HE SHOULD HAVE BEEN CAUSING HIS TAIL TO PROTRUDE INTO OUR AREA. THIS; HOWEVER; WAS NOT APPARENT TO ME AS IT WAS DARK AND IT IS NORMAL FOR US TO PARK CLOSE BY OTHER ACFT. WE HAVE TO RELY ON WING WALKERS AND THE 'STOP/GO' LIGHT PANEL AS WE CANNOT SEE THE WING TIPS FROM THE COCKPIT WITHOUT OPENING EITHER CLEARVIEW WINDOW. I FEEL THAT WE WERE FOLLOWING OUR GND PROCS AND THAT OUR PROCS ARE SAFE AND CORRECT. HAD OUR WING WALKER BEEN PAYING ATTN THEY WOULD HAVE SEEN THE OTHER ACFT AND WOULD HAVE PREVENTED US FROM APCHING THE GATE UNTIL THE AREA WAS CLR.