At 700 ft on an ILS final for ewr 4R; a dhc-8-400 localizer deviated left causing the autopilot to q...

Narrative:

We were cleared for the ILS 4R approach into ewr. I was utilizing the autopilot for the approach and at 700 feet AGL the pm called; 'approach lights' in sight. I continued to scan my pfd and noticed that the localizer started to move to the left. The autopilot quickly turned left to correct for this condition; but when I looked up; the runway lights and runway were slightly to my right. I immediately disengaged the autopilot to line up with the runway and continue a stabilized approach to landing. This seemed to be an anomaly with the reception of the localizer. The autopilot reacted as if something had gotten in between the aircraft and localizer because it is very strange that the localizer would indicate that we were right of course when the aircraft was left of course. It is important that pilots continue to hold the controls during approaches with an autopilot because of the quick reaction necessary to correct for potential hazards.

Original NASA ASRS Text

Title: At 700 FT on an ILS final for EWR 4R; a DHC-8-400 localizer deviated left causing the autopilot to quickly follow but the First Officer disconnected the autopilot; returned to course and continued to a safe landing.

Narrative: We were cleared for the ILS 4R approach into EWR. I was utilizing the autopilot for the approach and at 700 feet AGL the PM called; 'approach lights' in sight. I continued to scan my PFD and noticed that the localizer started to move to the left. The autopilot quickly turned left to correct for this condition; but when I looked up; the runway lights and runway were slightly to my right. I immediately disengaged the autopilot to line up with the runway and continue a stabilized approach to landing. This seemed to be an anomaly with the reception of the localizer. The autopilot reacted as if something had gotten in between the aircraft and localizer because it is very strange that the localizer would indicate that we were right of course when the aircraft was left of course. It is important that pilots continue to hold the controls during approaches with an autopilot because of the quick reaction necessary to correct for potential hazards.

Data retrieved from NASA's ASRS site 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.

Attributes
ACN	1141753
Time
Date	201401
Local Time Of Day	1201-1800
Place
Locale Reference	EWR.Airport
State Reference	NJ
Environment
Flight Conditions	Marginal
Light	Daylight
Aircraft 1
Make Model Name	Dash 8-400
Operating Under FAR Part	Part 121
Flight Phase	Final Approach
Flight Plan	IFR
Component
Aircraft Component	ILS/VOR
Person 1
Function	Pilot Flying First Officer
Person 2
Function	Pilot Not Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Track / Heading All Types

At 700 ft on an ILS final for ewr 4R; a dhc-8-400 localizer deviated left causing the autopilot to quickly follow but the first officer disconnected the autopilot; returned to course and continued to a safe landing.