Air carrier medium large transport on ILS approach advised by tower well left of course with both navigation sets showing on course and on glide shope. When autopilot disconnected ILS fail flags appeared.

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Attributes
ACN	81452
Time
Date	198802
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : atl
State Reference	GA
Altitude	msl bound lower : 2500 msl bound upper : 2500
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : atl tower : cvg
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	ils localizer & glide slope : atl
Flight Phase	descent : approach
Route In Use	approach : straight in
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : flight engineer pilot : cfi
Experience	flight time last 90 days : 200 flight time total : 5000 flight time type : 450
ASRS Report	81452
Person 2
Function	controller : local
Qualification	controller : radar
Events
Anomaly	other anomaly other other spatial deviation
Independent Detector	other controllera other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Navigational Facility
Air Traffic Incident	other

Narrative:

Established on ILS runway 27L atl on a 12 mile final, coupled approach, ILS identified on both receivers. All indications on course and normal. Glide slope intercept at 3500'msl. Upon passing 2700' MSL no outer marker indication. Switched MB receiver to high, still no indication. Upon passing a 2500' tower advises we are well left of course. Both CDI's and FD's show on localizer and GS. Disengage autopilot, flags appear on both locs and GS's. Initiated missed approach, broke out into VMC, landed on visual approach. Estimated 1/2 mi left of localizer course. Callback conversation with the reporter has revealed the following information: problem was reviewed with tower personnel and the fault was in the ILS localizer ground equipment. The fact that the flags in the cockpit came on as the autopilot was disconnected was a coincidence as the automatic monitor in the tower has a sequence it goes through prior to shutting down the ILS when it detects a fault. There has been no further follow up by the FAA.

Original NASA ASRS Text

Title: ACR MLG ON ILS APCH ADVISED BY TWR WELL LEFT OF COURSE WITH BOTH NAVIGATION SETS SHOWING ON COURSE AND ON GLIDE SHOPE. WHEN AUTOPILOT DISCONNECTED ILS FAIL FLAGS APPEARED.

Narrative: ESTABLISHED ON ILS RWY 27L ATL ON A 12 MILE FINAL, COUPLED APCH, ILS IDENTIFIED ON BOTH RECEIVERS. ALL INDICATIONS ON COURSE AND NORMAL. GLIDE SLOPE INTERCEPT AT 3500'MSL. UPON PASSING 2700' MSL NO OUTER MARKER INDICATION. SWITCHED MB RECEIVER TO HIGH, STILL NO INDICATION. UPON PASSING A 2500' TWR ADVISES WE ARE WELL LEFT OF COURSE. BOTH CDI'S AND FD'S SHOW ON LOC AND GS. DISENGAGE AUTOPILOT, FLAGS APPEAR ON BOTH LOCS AND GS'S. INITIATED MISSED APCH, BROKE OUT INTO VMC, LANDED ON VISUAL APCH. ESTIMATED 1/2 MI LEFT OF LOC COURSE. CALLBACK CONVERSATION WITH THE REPORTER HAS REVEALED THE FOLLOWING INFORMATION: PROBLEM WAS REVIEWED WITH TWR PERSONNEL AND THE FAULT WAS IN THE ILS LOC GND EQUIPMENT. THE FACT THAT THE FLAGS IN THE COCKPIT CAME ON AS THE AUTOPILOT WAS DISCONNECTED WAS A COINCIDENCE AS THE AUTOMATIC MONITOR IN THE TWR HAS A SEQUENCE IT GOES THROUGH PRIOR TO SHUTTING DOWN THE ILS WHEN IT DETECTS A FAULT. THERE HAS BEEN NO FURTHER FOLLOW UP BY THE FAA.

Data retrieved from NASA's ASRS site as of August 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.