AN ACR FK10 FLC MADE A GAR WHILE ON AN ILS APCH TO RWY 21R AT DTW DUE TO FULL SCALE DEFLECTION OF THE GS INDICATOR. A DC10 WAS JUST TOUCHING DOWN AT THE TIME AND MAY HAVE AFFECTED THE GS; BUT THE RPTR BELIEVES THAT THE BUILDINGS AND ACFT IN THE TERMINAL AREAS OF THE ARPT ALSO AFFECT THE SYS.

Narrative

ON APCH; INSIDE ILPUT FAF ILS RWY 21R AT DTW MADE A GAR BECAUSE OF A FULL SCALE DEFLECTION OF THE GS NEEDLE. WE WERE LNDG BEHIND A DC10. WX WAS LESS THAN 700 FT OVCST 1 3/4 MI VISIBILITY. ACFT BEHIND US RPTED SOME DEFLECTION ALSO. ON SECOND APCH TO SAME RWY SOME DEFLECTION WAS NOTICED IN THE SAME LOCATION; NOT ENOUGH FOR ANOTHER GAR. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THIS RPTR IS A FOKKER F100 CAPT WHO WAS MAKING AN ILS APCH IN IMC TO RWY 21R AT DTW WHEN; HE SAID; THE GS INDICATOR DEFLECTED FULL SCALE TO THE DOWN. THE FLC WAS FOLLOWING AN ACR DC10 WHICH HAD JUST TOUCHED DOWN. THE RPTR STATED THAT HE HEARD THE DC10 CALL THAT HE WAS ON THE RWY JUST AFTER THE DEFLECTION STARTED. HE SAID THAT HE WAS ABOUT 5 OR 6 NM BEHIND THE DC10 AND STARTED HIS GAR AT ABOUT THE FAF. DURING THE GAR HE NOTED THAT THE GS DID MOVE UP AND DOWN. THE RPTR BRIEFED THE FO THAT HE WOULD ATTEMPT TO MAKE ANOTHER APCH; BUT THAT HE WOULD GAR IF THERE WERE ANOTHER FULL DEFLECTION AND THEN TRY AN APCH TO ANOTHER RWY. HE SAID THAT ON THE SECOND APCH HE HAND FLEW THE ACFT AND; THOUGH THERE WERE SOME LESS SERIOUS DEFLECTIONS; MADE A SUCCESSFUL LNDG. THE RPTR SAID THAT HE HAS REVIEWED THE SIT AND HE BELIEVES THAT THE DC10 WAS; IN PART; RESPONSIBLE FOR THE DEFLECTIONS; BUT HE NOW THINKS THAT THE TERMINAL BUILDINGS ON THE L OF THE APCH COURSE AND THE LARGE CARGO FACILITY BUILDINGS ON THE R AND THE ACFT THAT OPERATE AROUND THEM SHARE IN THE EFFECT ON THE GS SIGNAL. HE SAID THAT ON HIS SECOND APCH THE DC10 WAS NO FACTOR; YET HE STILL HAD SOME DEFLECTIONS. ALSO THE DC10 WAS NO FACTOR FOR THE ACFT THAT FOLLOWED HIM DURING THE FIRST APCH AND THAT ALSO RPTED LESS SERIOUS DEFLECTIONS.