A B737-300 flight crew experiences an unreliable localizer during an ILS approach into jackson hole, wy. The WX was fortunately VMC with the airport and runway in sight during this approach. Another aircraft verified the localizer course problem. Crew reported this event to ZLC controller.

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Attributes
ACN	394501
Time
Date	199802
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : jac
State Reference	WY
Altitude	msl bound lower : 12000 msl bound upper : 12000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zlc
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : jac Other Other
Flight Phase	descent : approach descent other
Route In Use	arrival other enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	cruise other other
Route In Use	enroute other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 234 flight time total : 11000
ASRS Report	394501
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	none taken : unable other
Consequence	Other
Supplementary
Primary Problem	Navigational Facility
Air Traffic Incident	other
Situations
Navigational Aid	Unspecified

Narrative:

Clearance was issued to conduct an ILS approach to runway 18 at jac airport from the en route airway system. After the turn to final at 12000 ft MSL, the ILS final approach course was commenced. After operating in LNAV to intercept the course, guidance was switched to the ILS mode for tracking and descent to the airport. After tracking for a short time to the FAF it was determined that the localizer was unreliable, but the GS was reliable. After reporting this condition to ZLC, the approach was continued visually (airport and runway in sight throughout approach) to an uneventful landing. ZLC was surprised to hear about the malfunction and asked another carrier to monitor the ILS also. This confirmed the problem with the ILS. I surmise that the approach is not monitored for the purposes of NOTAMS. Additionally, a NOTAM check afterward indicated no problems with the ILS. Callback conversation with reporter revealed the following information: reporter was flying a B737-300. The other aircraft was an FMC equipped aircraft. Jac, wy, is a CTAF non tower airport. PIC had reported this problem to ZLC only and does not know anything more about this situation. He stated that he was in VMC conditions.

Original NASA ASRS Text

Title: A B737-300 FLC EXPERIENCES AN UNRELIABLE LOC DURING AN ILS APCH INTO JACKSON HOLE, WY. THE WX WAS FORTUNATELY VMC WITH THE ARPT AND RWY IN SIGHT DURING THIS APCH. ANOTHER ACFT VERIFIED THE LOC COURSE PROB. CREW RPTED THIS EVENT TO ZLC CTLR.

Narrative: CLRNC WAS ISSUED TO CONDUCT AN ILS APCH TO RWY 18 AT JAC ARPT FROM THE ENRTE AIRWAY SYS. AFTER THE TURN TO FINAL AT 12000 FT MSL, THE ILS FINAL APCH COURSE WAS COMMENCED. AFTER OPERATING IN LNAV TO INTERCEPT THE COURSE, GUIDANCE WAS SWITCHED TO THE ILS MODE FOR TRACKING AND DSCNT TO THE ARPT. AFTER TRACKING FOR A SHORT TIME TO THE FAF IT WAS DETERMINED THAT THE LOC WAS UNRELIABLE, BUT THE GS WAS RELIABLE. AFTER RPTING THIS CONDITION TO ZLC, THE APCH WAS CONTINUED VISUALLY (ARPT AND RWY IN SIGHT THROUGHOUT APCH) TO AN UNEVENTFUL LNDG. ZLC WAS SURPRISED TO HEAR ABOUT THE MALFUNCTION AND ASKED ANOTHER CARRIER TO MONITOR THE ILS ALSO. THIS CONFIRMED THE PROB WITH THE ILS. I SURMISE THAT THE APCH IS NOT MONITORED FOR THE PURPOSES OF NOTAMS. ADDITIONALLY, A NOTAM CHK AFTERWARD INDICATED NO PROBS WITH THE ILS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR WAS FLYING A B737-300. THE OTHER ACFT WAS AN FMC EQUIPPED ACFT. JAC, WY, IS A CTAF NON TWR ARPT. PIC HAD RPTED THIS PROB TO ZLC ONLY AND DOES NOT KNOW ANYTHING MORE ABOUT THIS SIT. HE STATED THAT HE WAS IN VMC CONDITIONS.

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