A C172 conducting an approach to lse received a false localizer signal.

Attributes
ACN	645567
Time
Date	200501
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : lse.airport
State Reference	WI
Altitude	msl single value : 4000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zmp.artcc
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Navigation In Use	ils localizer & glide slope : 18
Flight Phase	descent : approach
Route In Use	approach : instrument precision arrival : on vectors
Flight Plan	IFR
Person 1
Affiliation	other
Function	instruction : instructor
Qualification	pilot : commercial pilot : cfi pilot : instrument
Experience	flight time last 90 days : 60 flight time total : 825 flight time type : 675
ASRS Report	645567
Person 2
Affiliation	other
Function	flight crew : single pilot
Events
Anomaly	aircraft equipment problem : critical non adherence : clearance non adherence : published procedure other spatial deviation
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to original clearance none taken : anomaly accepted
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Aircraft Navigational Facility
Primary Problem	Navigational Facility

Narrative:

Tracking the 14 DME arc to lse with a student in IFR training we received what we believed to be a localizer signal; and turned inbound as the instruments indicated. Being in VMC conditions; we quickly realized that there was something wrong. All frequencys were correct; tuned in 2ND VOR navigation in the airplane and received the same indication again. We believe at this time we were receiving a false localizer indication due to the reaction of the CDI on both VOR navs. We continued to fly the arc visually now but by this time we were well inside the 14 DME arc by 5 miles (9.2 from NAVAID). Altitude clearances were maintained; but approach course wasn't tracked correctly due to false indications from the localizer signal. We did obtain a new correct signal farther into the approach and were able to complete the approach successfully. WX conditions were VMC throughout this time frame. Callback conversation with reporter revealed the following information: reporter stated that she and the other pilot are familiar with the airport area and consequently knew the localizer signal was incorrect. They estimated that the signal was off by as much as 20 degrees. They had approached from the west; dscnded and then climbed back to 4000 ft for traffic. A 2449 ft antenna obstacle exists in that quadrant. They saw the antenna because they were VFR; knew where the antenna was located; and therefore it was not a problem. In full IMC conditions at a lower altitude; she felt this could have been a different story. ATC had no comments to them about their approach track.

Original NASA ASRS Text

Title: A C172 CONDUCTING AN APCH TO LSE RECEIVED A FALSE LOCALIZER SIGNAL.

Narrative: TRACKING THE 14 DME ARC TO LSE WITH A STUDENT IN IFR TRAINING WE RECEIVED WHAT WE BELIEVED TO BE A LOCALIZER SIGNAL; AND TURNED INBND AS THE INSTRUMENTS INDICATED. BEING IN VMC CONDITIONS; WE QUICKLY REALIZED THAT THERE WAS SOMETHING WRONG. ALL FREQS WERE CORRECT; TUNED IN 2ND VOR NAV IN THE AIRPLANE AND RECEIVED THE SAME INDICATION AGAIN. WE BELIEVE AT THIS TIME WE WERE RECEIVING A FALSE LOCALIZER INDICATION DUE TO THE REACTION OF THE CDI ON BOTH VOR NAVS. WE CONTINUED TO FLY THE ARC VISUALLY NOW BUT BY THIS TIME WE WERE WELL INSIDE THE 14 DME ARC BY 5 MILES (9.2 FROM NAVAID). ALT CLEARANCES WERE MAINTAINED; BUT APCH COURSE WASN'T TRACKED CORRECTLY DUE TO FALSE INDICATIONS FROM THE LOCALIZER SIGNAL. WE DID OBTAIN A NEW CORRECT SIGNAL FARTHER INTO THE APCH AND WERE ABLE TO COMPLETE THE APCH SUCCESSFULLY. WX CONDITIONS WERE VMC THROUGHOUT THIS TIME FRAME. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT SHE AND THE OTHER PLT ARE FAMILIAR WITH THE ARPT AREA AND CONSEQUENTLY KNEW THE LOCALIZER SIGNAL WAS INCORRECT. THEY ESTIMATED THAT THE SIGNAL WAS OFF BY AS MUCH AS 20 DEGS. THEY HAD APCHED FROM THE WEST; DSCNDED AND THEN CLBED BACK TO 4000 FT FOR TFC. A 2449 FT ANTENNA OBSTACLE EXISTS IN THAT QUADRANT. THEY SAW THE ANTENNA BECAUSE THEY WERE VFR; KNEW WHERE THE ANTENNA WAS LOCATED; AND THEREFORE IT WAS NOT A PROB. IN FULL IMC CONDITIONS AT A LOWER ALT; SHE FELT THIS COULD HAVE BEEN A DIFFERENT STORY. ATC HAD NO COMMENTS TO THEM ABOUT THEIR APCH TRACK.

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.