Narrative:

Callback conversation with reporter revealed the following information: the reporter stated that map shift problem was caused by duplicate ILS/DME broadcasting on the same frequency, but physically located at different positions. The reporter said this explanation and data was given to him by the fleet manager who received this data from the manufacturer of the flight management system letter from manufacturer: potential position error caused by duplicate frequency ILS/DME. We recently received a report of a position error into phx. This relates to the multiple ILS/DME's broadcasting on the same frequency but are physically located at different positions. When certain honeywell legacy FMS encounter this condition, the potential exists for a position error. When flying near the airports that contain these types of ILS/DME facilities, it is possible that the FMS may tune a frequency for a radio position calculation belonging to one of the multiple DME's. Once tuned, the slant range returned from the DME could be associated with a different DME location than that expected by the FMS (i.e., the DME located at the opposite end of the runway). Honeywell has removed the DME portion of these ILS/DME's from the navigation database thus addressing the potential for position error. Removing the DME portion of the ILS/DME's from the navigation database will cause the FMS to eliminate DME tuning for those facilities. Therefore, DME distance information associated with these ILS/DME's will not be utilized by the FMS for a position calculation or distance display. The associated ILS data will remain in the navigation database and will not be affected by this change. Although this potential position error was first reported in november 2002, recent changes to the phx ILS/DME facilities allowed the DME portion of ILS/DME facility back into the navigation database. Honeywell has completed an extensive search of the navigation data library and determined that only the DME's of the following ILS/DME facilities at phx have this potential for position error: iaha, icwj, and iphx. All other duplicate frequency ILS/DME facilities have been removed. Please see the complete list in the attachment. Please note that we have identified your navigation database as having this potential for position error therefore we have generated a navigation database for you to download and load into your aircraft. To address this issue going forward, we have amended our production process to search for this data configuration and remove the DME portion from the navigation database prior to selection. Duplicate frequency list: bed: ibed, iulj. Bos: ilip, imdc. Gtb: iaez, igtb. Iah: ibzu, iond. Lax: icfn, igpe, ihqb, iias, ilax, imkz, ioss, iuwu. Mci: irni, iuqy. Mht: imna. Mia: icnv, iroy. Mry: imry, imtb. Phx: iaha, icwj, iphx. San: isan, iubr. Stp: ibao, ivkg. Xna: ifbs, ixna.

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Original NASA ASRS Text

Title: A B757-200 RPTS A NAVIGATION MAP SHIFT ON LNDG AT PHX. CAUSED BY DUPLICATE FREQ ILS-DME FREQ AT DIFFERENT POSITIONS.

Narrative: CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT MAP SHIFT PROB WAS CAUSED BY DUPLICATE ILS/DME BROADCASTING ON THE SAME FREQ, BUT PHYSICALLY LOCATED AT DIFFERENT POSITIONS. THE RPTR SAID THIS EXPLANATION AND DATA WAS GIVEN TO HIM BY THE FLEET MANAGER WHO RECEIVED THIS DATA FROM THE MANUFACTURER OF THE FLT MANAGEMENT SYSTEM LETTER FROM MANUFACTURER: POTENTIAL POSITION ERROR CAUSED BY DUPLICATE FREQ ILS/DME. WE RECENTLY RECEIVED A RPT OF A POSITION ERROR INTO PHX. THIS RELATES TO THE MULTIPLE ILS/DME'S BROADCASTING ON THE SAME FREQ BUT ARE PHYSICALLY LOCATED AT DIFFERENT POSITIONS. WHEN CERTAIN HONEYWELL LEGACY FMS ENCOUNTER THIS CONDITION, THE POTENTIAL EXISTS FOR A POSITION ERROR. WHEN FLYING NEAR THE ARPTS THAT CONTAIN THESE TYPES OF ILS/DME FACILITIES, IT IS POSSIBLE THAT THE FMS MAY TUNE A FREQ FOR A RADIO POSITION CALCULATION BELONGING TO ONE OF THE MULTIPLE DME'S. ONCE TUNED, THE SLANT RANGE RETURNED FROM THE DME COULD BE ASSOCIATED WITH A DIFFERENT DME LOCATION THAN THAT EXPECTED BY THE FMS (I.E., THE DME LOCATED AT THE OPPOSITE END OF THE RWY). HONEYWELL HAS REMOVED THE DME PORTION OF THESE ILS/DME'S FROM THE NAVIGATION DATABASE THUS ADDRESSING THE POTENTIAL FOR POSITION ERROR. REMOVING THE DME PORTION OF THE ILS/DME'S FROM THE NAVIGATION DATABASE WILL CAUSE THE FMS TO ELIMINATE DME TUNING FOR THOSE FACILITIES. THEREFORE, DME DISTANCE INFO ASSOCIATED WITH THESE ILS/DME'S WILL NOT BE UTILIZED BY THE FMS FOR A POSITION CALCULATION OR DISTANCE DISPLAY. THE ASSOCIATED ILS DATA WILL REMAIN IN THE NAVIGATION DATABASE AND WILL NOT BE AFFECTED BY THIS CHANGE. ALTHOUGH THIS POTENTIAL POSITION ERROR WAS FIRST RPTED IN NOVEMBER 2002, RECENT CHANGES TO THE PHX ILS/DME FACILITIES ALLOWED THE DME PORTION OF ILS/DME FACILITY BACK INTO THE NAVIGATION DATABASE. HONEYWELL HAS COMPLETED AN EXTENSIVE SEARCH OF THE NAVIGATION DATA LIBRARY AND DETERMINED THAT ONLY THE DME'S OF THE FOLLOWING ILS/DME FACILITIES AT PHX HAVE THIS POTENTIAL FOR POSITION ERROR: IAHA, ICWJ, AND IPHX. ALL OTHER DUPLICATE FREQ ILS/DME FACILITIES HAVE BEEN REMOVED. PLEASE SEE THE COMPLETE LIST IN THE ATTACHMENT. PLEASE NOTE THAT WE HAVE IDENTIFIED YOUR NAVIGATION DATABASE AS HAVING THIS POTENTIAL FOR POSITION ERROR THEREFORE WE HAVE GENERATED A NAVIGATION DATABASE FOR YOU TO DOWNLOAD AND LOAD INTO YOUR ACFT. TO ADDRESS THIS ISSUE GOING FORWARD, WE HAVE AMENDED OUR PRODUCTION PROCESS TO SEARCH FOR THIS DATA CONFIGURATION AND REMOVE THE DME PORTION FROM THE NAVIGATION DATABASE PRIOR TO SELECTION. DUPLICATE FREQ LIST: BED: IBED, IULJ. BOS: ILIP, IMDC. GTB: IAEZ, IGTB. IAH: IBZU, IOND. LAX: ICFN, IGPE, IHQB, IIAS, ILAX, IMKZ, IOSS, IUWU. MCI: IRNI, IUQY. MHT: IMNA. MIA: ICNV, IROY. MRY: IMRY, IMTB. PHX: IAHA, ICWJ, IPHX. SAN: ISAN, IUBR. STP: IBAO, IVKG. XNA: IFBS, IXNA.

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.