Narrative:

Experienced runway 4R localizer deflection at 20 mi from ord VOR/DME. Autoplt responded to localizer deflection and was disconnected. Approximately deflection was less than 1/3 DOT deflection. Localizer steadied as approach continued. Callback conversation with reporter revealed the following information: the captain said that all of his company's flight plans have information regarding the airport and the route included on the plan. This airport always has a note about this approach advising the crew that these deflections have been occurring. Unlike some of the later aircraft that have a damping logic in the autoflt system, the MD80 series will attempt to follow the rapidly moving localizer on the approach as it moves left to right according to the reporter. He said that the only solution is to disconnect the autoplt and hand fly it until the localizer settles down. As the crew got closer to the airport they saw a company MD80 that had landed before them taxiing in. They felt that the MD80 had caused the interference with the localizer signal also as the aircraft got closer to the airport the localizer course display showed little or not rapid deflection. The reporter said that he suspects that the deflections are caused by aircraft as they rollout on the runway. He feels that these aircraft deflect or otherwise interfere with the signal and he thinks that relocating the antenna may help solve the problem.

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Original NASA ASRS Text

Title: AN ACR MD80 FLC RPTS THAT THEY HAD DEFLECTIONS IN THE RWY 4R LOC AT ABOUT 20 NM FROM THE ARPT DURING AN APCH. THE ACFT'S AUTOFLT SYS ATTEMPTED TO FOLLOW THE L AND R DEFLECTIONS.

Narrative: EXPERIENCED RWY 4R LOC DEFLECTION AT 20 MI FROM ORD VOR/DME. AUTOPLT RESPONDED TO LOC DEFLECTION AND WAS DISCONNECTED. APPROX DEFLECTION WAS LESS THAN 1/3 DOT DEFLECTION. LOC STEADIED AS APCH CONTINUED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CAPT SAID THAT ALL OF HIS COMPANY'S FLT PLANS HAVE INFO REGARDING THE ARPT AND THE RTE INCLUDED ON THE PLAN. THIS ARPT ALWAYS HAS A NOTE ABOUT THIS APCH ADVISING THE CREW THAT THESE DEFLECTIONS HAVE BEEN OCCURRING. UNLIKE SOME OF THE LATER ACFT THAT HAVE A DAMPING LOGIC IN THE AUTOFLT SYS, THE MD80 SERIES WILL ATTEMPT TO FOLLOW THE RAPIDLY MOVING LOC ON THE APCH AS IT MOVES L TO R ACCORDING TO THE RPTR. HE SAID THAT THE ONLY SOLUTION IS TO DISCONNECT THE AUTOPLT AND HAND FLY IT UNTIL THE LOC SETTLES DOWN. AS THE CREW GOT CLOSER TO THE ARPT THEY SAW A COMPANY MD80 THAT HAD LANDED BEFORE THEM TAXIING IN. THEY FELT THAT THE MD80 HAD CAUSED THE INTERFERENCE WITH THE LOC SIGNAL ALSO AS THE ACFT GOT CLOSER TO THE ARPT THE LOC COURSE DISPLAY SHOWED LITTLE OR NOT RAPID DEFLECTION. THE RPTR SAID THAT HE SUSPECTS THAT THE DEFLECTIONS ARE CAUSED BY ACFT AS THEY ROLLOUT ON THE RWY. HE FEELS THAT THESE ACFT DEFLECT OR OTHERWISE INTERFERE WITH THE SIGNAL AND HE THINKS THAT RELOCATING THE ANTENNA MAY HELP SOLVE THE PROB.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.