Narrative:

Cleared for ILS runway 9R ord with parallel ILS runway 9L approachs in progress with approach monitor active. WX reported: 070/13 5SM -RA br 007BKN 014OVC. Radios tuned and idented with strong identify to ord ILS runway 9R 111.1. From southern downwind; ATC gave us 060 degree heading to intercept ILS runway 9R and cleared us for the ILS runway 9R approach at 4000 ft. In heading mode first officer (PF) set heading to 060 degrees and armed approach mode with the autoplt on and coupled to the flight director. After localizer came alive and corresponding flight director capture; both captain and first officer localizer HSI needles started deviating back to the left with the autoplt making corresponding corrections to the left (it was 'captured' at this point). Both localizer's then swung from left of center to right of center with flight director commanding and autoplt executing a rolling turn back to the right; chasing the HSI. First officer disconnected the autoplt to prevent excessive bank and heading changes; placed flight director into heading mode and took up approximately a 100 degree heading. Simultaneous with autoplt disconnect and heading mode selection; ATC approach monitor stated that we were left of course and issued a right turn away from runway 9L to a heading of 120 degrees and a climb to 5000 ft. We were handed off to approach control for vectors to another runway 9R ILS. We reported localizer problems to approach and he indicated that no other aircraft had reported any ILS deviations or problems. We were vectored for another ILS runway 9R approach but this time ATC provided increased separation by placing us solo on runway 9R with no parallel runway 9L traffic. Similar simultaneous localizer deviations occurred at approximately 10 DME outside of deana with deviations ceasing as we approached deana. Completed second attempted ILS runway 9R without further incident. Upon reaching the gate; maintenance log entry was made reporting repeated localizer deviations. TCAS was on and active at time of localizer deviation; and no TA or RA was issued. ATC reported no separation conflict. We believe this event occurred as a result of unexplained and repeated (both approachs) localizer needle swings to the left and right of center with corresponding autoplt corrections which initially chased the false localizer indication to the north of course. Our instrument scan provided the first indication that the event had occurred along with abnormal autoplt commanded banking and heading changes to the left and right as it tried to maintain the errant localizer indication. Subsequent notification by ATC that we were north of course confirmed this. With knowledge of simultaneous approachs in effect to runway 9L; both flight crew and ATC directed actions to turn the aircraft to the south were initiated. Upon recognition that the flight director was commanding excessive bank angle and heading changes to attempt recapture of the errant localizer signal; the first officer disconnected the autoplt and began to roll the aircraft out of the bank and took up a heading of approximately 110 degrees. Simultaneously; the captain selected heading mode at the first officer's request and selected the heading with the heading bug. Captain then verified that the deviations were present in both pilot's HSI indications with an instrument xchk. Captain communicated problem with ATC who then issued the climb out and turn instructions. I suggest that the cause of localizer swings and errant flight director commands in the embraer 145 be idented and corrected. This seems to be a recurrent problem specific to the fleet type and seems to occur at 12-15 DME from the localizer and then subside closer to the marker.

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Original NASA ASRS Text

Title: EMB145 CREW REPORTS LOC OSCILLATIONS DURING RWY 9R ILS PRM AT ORD.

Narrative: CLRED FOR ILS RWY 9R ORD WITH PARALLEL ILS RWY 9L APCHS IN PROGRESS WITH APCH MONITOR ACTIVE. WX RPTED: 070/13 5SM -RA BR 007BKN 014OVC. RADIOS TUNED AND IDENTED WITH STRONG IDENT TO ORD ILS RWY 9R 111.1. FROM SOUTHERN DOWNWIND; ATC GAVE US 060 DEG HDG TO INTERCEPT ILS RWY 9R AND CLRED US FOR THE ILS RWY 9R APCH AT 4000 FT. IN HDG MODE FO (PF) SET HDG TO 060 DEGS AND ARMED APCH MODE WITH THE AUTOPLT ON AND COUPLED TO THE FLT DIRECTOR. AFTER LOC CAME ALIVE AND CORRESPONDING FLT DIRECTOR CAPTURE; BOTH CAPT AND FO LOC HSI NEEDLES STARTED DEVIATING BACK TO THE L WITH THE AUTOPLT MAKING CORRESPONDING CORRECTIONS TO THE L (IT WAS 'CAPTURED' AT THIS POINT). BOTH LOC'S THEN SWUNG FROM L OF CTR TO R OF CTR WITH FLT DIRECTOR COMMANDING AND AUTOPLT EXECUTING A ROLLING TURN BACK TO THE R; CHASING THE HSI. FO DISCONNECTED THE AUTOPLT TO PREVENT EXCESSIVE BANK AND HDG CHANGES; PLACED FLT DIRECTOR INTO HDG MODE AND TOOK UP APPROX A 100 DEG HDG. SIMULTANEOUS WITH AUTOPLT DISCONNECT AND HDG MODE SELECTION; ATC APCH MONITOR STATED THAT WE WERE L OF COURSE AND ISSUED A R TURN AWAY FROM RWY 9L TO A HDG OF 120 DEGS AND A CLB TO 5000 FT. WE WERE HANDED OFF TO APCH CTL FOR VECTORS TO ANOTHER RWY 9R ILS. WE RPTED LOC PROBS TO APCH AND HE INDICATED THAT NO OTHER ACFT HAD RPTED ANY ILS DEVS OR PROBS. WE WERE VECTORED FOR ANOTHER ILS RWY 9R APCH BUT THIS TIME ATC PROVIDED INCREASED SEPARATION BY PLACING US SOLO ON RWY 9R WITH NO PARALLEL RWY 9L TFC. SIMILAR SIMULTANEOUS LOC DEVS OCCURRED AT APPROX 10 DME OUTSIDE OF DEANA WITH DEVS CEASING AS WE APCHED DEANA. COMPLETED SECOND ATTEMPTED ILS RWY 9R WITHOUT FURTHER INCIDENT. UPON REACHING THE GATE; MAINT LOG ENTRY WAS MADE REPORTING REPEATED LOC DEVS. TCAS WAS ON AND ACTIVE AT TIME OF LOC DEV; AND NO TA OR RA WAS ISSUED. ATC RPTED NO SEPARATION CONFLICT. WE BELIEVE THIS EVENT OCCURRED AS A RESULT OF UNEXPLAINED AND REPEATED (BOTH APCHS) LOC NEEDLE SWINGS TO THE L AND R OF CTR WITH CORRESPONDING AUTOPLT CORRECTIONS WHICH INITIALLY CHASED THE FALSE LOC INDICATION TO THE N OF COURSE. OUR INST SCAN PROVIDED THE FIRST INDICATION THAT THE EVENT HAD OCCURRED ALONG WITH ABNORMAL AUTOPLT COMMANDED BANKING AND HDG CHANGES TO THE L AND R AS IT TRIED TO MAINTAIN THE ERRANT LOC INDICATION. SUBSEQUENT NOTIFICATION BY ATC THAT WE WERE N OF COURSE CONFIRMED THIS. WITH KNOWLEDGE OF SIMULTANEOUS APCHS IN EFFECT TO RWY 9L; BOTH FLT CREW AND ATC DIRECTED ACTIONS TO TURN THE ACFT TO THE S WERE INITIATED. UPON RECOGNITION THAT THE FLT DIRECTOR WAS COMMANDING EXCESSIVE BANK ANGLE AND HDG CHANGES TO ATTEMPT RECAPTURE OF THE ERRANT LOC SIGNAL; THE FO DISCONNECTED THE AUTOPLT AND BEGAN TO ROLL THE ACFT OUT OF THE BANK AND TOOK UP A HDG OF APPROX 110 DEGS. SIMULTANEOUSLY; THE CAPT SELECTED HDG MODE AT THE FO'S REQUEST AND SELECTED THE HDG WITH THE HDG BUG. CAPT THEN VERIFIED THAT THE DEVS WERE PRESENT IN BOTH PLT'S HSI INDICATIONS WITH AN INST XCHK. CAPT COMMUNICATED PROB WITH ATC WHO THEN ISSUED THE CLBOUT AND TURN INSTRUCTIONS. I SUGGEST THAT THE CAUSE OF LOC SWINGS AND ERRANT FLT DIRECTOR COMMANDS IN THE EMBRAER 145 BE IDENTED AND CORRECTED. THIS SEEMS TO BE A RECURRENT PROB SPECIFIC TO THE FLEET TYPE AND SEEMS TO OCCUR AT 12-15 DME FROM THE LOC AND THEN SUBSIDE CLOSER TO THE MARKER.

Data retrieved from NASA's ASRS site as of January 2009 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.