Narrative:

I was manually flying a igs runway 13 approach into kai tak airport as captain of an air carrier-a widebody transport aircraft when we experienced a large map shift on the navigation display and deviated right of the localizer course. This map shift problem has occurred numerous times with the widebody transport at kai tak airport to air carrier-a, air carrier-B and air carrier-C airlines. Please see two memos to/from customer service manager, about the incorrect charting of a navigation aid (pou). Since the widebody transport FMS utilizes VOR DME data to update map display, it is possible that incorrect location of pou could cause this map shift. Air carrier-a has issued a NOTAM which requires the manual turning of navigation aids during this approach to eliminate this map shift problem. We accomplished this procedure prior to this approach but still experienced a large map shift. Because of the prior problem associated with this approach I decided to fly a raw data localizer approach. The first officer tuned all navigation aids including kl localizer manually and idented them aurally. The FMC has the ability to identify navigation aids and display the identifier visually. On turning inbound after passing lt NDB I observed the map display depiction of the localizer course considerably right of our position and the raw data localizer course 1/2 scale deflection left. The first officer advised the FMC was displaying the wrong identifier for the localizer so we doubted the validity of the raw data localizer. I turned the aircraft to the right towards the map display localizer course and asked him to query hong kong radar about our position. There was some delay getting a reply and we deviated considerably right of the actual localizer course before being given a turn northeast. After being turned on course by the hong kong radar we found ourselves centered on the raw data localizer which now displayed the correct identifier. The map display localizer was still several mi right of course. We completed the approach and landed uneventfully. I spoke with the hong kong approach watch supervisor concerning our deviation from final approach course. Callback conversation with reporter revealed following information. This situation known to exist for some time and is apparently unique to this widebody transport. Problem is suspected to originate with the position information being acquired by the FMC or perhaps an unknown data base error. Manual tuning and raw data approachs thought to be adequate protection from problem but apparently not so in this case. Supplemental information from acn 137337. I was briefed the next morning in hkg by a representative that some radio navigation aids from mainland china (pou) were being incorrectly used to update the IRS.

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Original NASA ASRS Text

Title: TRACK DEVIATION.

Narrative: I WAS MANUALLY FLYING A IGS RWY 13 APCH INTO KAI TAK ARPT AS CAPT OF AN ACR-A WDB ACFT WHEN WE EXPERIENCED A LARGE MAP SHIFT ON THE NAV DISPLAY AND DEVIATED RIGHT OF THE LOC COURSE. THIS MAP SHIFT PROB HAS OCCURRED NUMEROUS TIMES WITH THE WDB AT KAI TAK ARPT TO ACR-A, ACR-B AND ACR-C AIRLINES. PLEASE SEE TWO MEMOS TO/FROM CUSTOMER SVC MGR, ABOUT THE INCORRECT CHARTING OF A NAV AID (POU). SINCE THE WDB FMS UTILIZES VOR DME DATA TO UPDATE MAP DISPLAY, IT IS POSSIBLE THAT INCORRECT LOCATION OF POU COULD CAUSE THIS MAP SHIFT. ACR-A HAS ISSUED A NOTAM WHICH REQUIRES THE MANUAL TURNING OF NAV AIDS DURING THIS APCH TO ELIMINATE THIS MAP SHIFT PROB. WE ACCOMPLISHED THIS PROC PRIOR TO THIS APCH BUT STILL EXPERIENCED A LARGE MAP SHIFT. BECAUSE OF THE PRIOR PROB ASSOCIATED WITH THIS APCH I DECIDED TO FLY A RAW DATA LOC APCH. THE F/O TUNED ALL NAV AIDS INCLUDING KL LOC MANUALLY AND IDENTED THEM AURALLY. THE FMC HAS THE ABILITY TO IDENT NAV AIDS AND DISPLAY THE IDENTIFIER VISUALLY. ON TURNING INBND AFTER PASSING LT NDB I OBSERVED THE MAP DISPLAY DEPICTION OF THE LOC COURSE CONSIDERABLY RIGHT OF OUR POS AND THE RAW DATA LOC COURSE 1/2 SCALE DEFLECTION LEFT. THE F/O ADVISED THE FMC WAS DISPLAYING THE WRONG IDENTIFIER FOR THE LOC SO WE DOUBTED THE VALIDITY OF THE RAW DATA LOC. I TURNED THE ACFT TO THE RIGHT TOWARDS THE MAP DISPLAY LOC COURSE AND ASKED HIM TO QUERY HONG KONG RADAR ABOUT OUR POS. THERE WAS SOME DELAY GETTING A REPLY AND WE DEVIATED CONSIDERABLY RIGHT OF THE ACTUAL LOC COURSE BEFORE BEING GIVEN A TURN NE. AFTER BEING TURNED ON COURSE BY THE HONG KONG RADAR WE FOUND OURSELVES CENTERED ON THE RAW DATA LOC WHICH NOW DISPLAYED THE CORRECT IDENTIFIER. THE MAP DISPLAY LOC WAS STILL SEVERAL MI RIGHT OF COURSE. WE COMPLETED THE APCH AND LANDED UNEVENTFULLY. I SPOKE WITH THE HONG KONG APCH WATCH SUPVR CONCERNING OUR DEVIATION FROM FINAL APCH COURSE. CALLBACK CONVERSATION WITH RPTR REVEALED FOLLOWING INFO. THIS SITUATION KNOWN TO EXIST FOR SOME TIME AND IS APPARENTLY UNIQUE TO THIS WDB. PROB IS SUSPECTED TO ORIGINATE WITH THE POS INFO BEING ACQUIRED BY THE FMC OR PERHAPS AN UNKNOWN DATA BASE ERROR. MANUAL TUNING AND RAW DATA APCHS THOUGHT TO BE ADEQUATE PROTECTION FROM PROB BUT APPARENTLY NOT SO IN THIS CASE. SUPPLEMENTAL INFO FROM ACN 137337. I WAS BRIEFED THE NEXT MORNING IN HKG BY A REPRESENTATIVE THAT SOME RADIO NAV AIDS FROM MAINLAND CHINA (POU) WERE BEING INCORRECTLY USED TO UPDATE THE IRS.

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.