The flight crew of an undisclosed aircraft type initiated a go around when erratic ILS signals resul...

Narrative:

We were on approach to 18R clt when after joining up on the auto pilot there were some erratic indications on the localizer. The plane would bank left and right 5 to 10 degrees due to sudden movements of the localizer. During the whole approach there was good identification of the ILS via the pfd. The first officer decided to [follow?] the erratic indication and the sudden movements the autopilot would make.after glide slope intercept the first officer reached task saturation due to this erratic information and then went full scale low on the glide slope causing a low altitude alert. Another approach was made with little to no erratic information from the same ILS. I am not sure what is causing this (aircraft or ground equipment?) but I have seen such erratic information displayed several times on 18R and 5 in clt. It is not every flight and every approach as is evident by the second approach to the same runway and little to no problem with the indications. Such erratic indications can lead to mistrust of information and task saturation quickly.

Original NASA ASRS Text

Title: The flight crew of an undisclosed aircraft type initiated a go around when erratic ILS signals resulted in a low altitude alert from the CLT Tower. A second approach was made with normal ILS signals.

Narrative: We were on approach to 18R CLT when after joining up on the auto pilot there were some erratic indications on the localizer. The plane would bank left and right 5 to 10 degrees due to sudden movements of the localizer. During the whole approach there was good identification of the ILS via the PFD. The First Officer decided to [follow?] the erratic indication and the sudden movements the autopilot would make.After glide slope intercept the First Officer reached task saturation due to this erratic information and then went full scale low on the glide slope causing a low altitude alert. Another approach was made with little to no erratic information from the same ILS. I am not sure what is causing this (aircraft or ground equipment?) but I have seen such erratic information displayed several times on 18R and 5 in CLT. It is not every flight and every approach as is evident by the second approach to the same runway and little to no problem with the indications. Such erratic indications can lead to mistrust of information and task saturation quickly.

Data retrieved from NASA's ASRS site as of April 2012 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	915756
Time
Date	201010
Local Time Of Day	1201-1800
Place
Locale Reference	CLT.Airport
State Reference	NC
Environment
Flight Conditions	IMC
Aircraft 1
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Component
Aircraft Component	ILS/VOR
Person 1
Function	Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe Inflight Event / Encounter Unstabilized Approach

The flight crew of an undisclosed aircraft type initiated a go around when erratic ILS signals resulted in a low altitude alert from the clt tower. A second approach was made with normal ILS signals.