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B757 aircraft on STAR and descent had map shift which reporter captain attributes to the lax DME. Reporter claims that his raw data showed accurate DME, but the FMS was 2 mi off.
| Attributes | |
| ACN | 395411 |
| Time | |
| Date | 199803 |
| Day | Tue |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | atc facility : lax |
| State Reference | CA |
| Altitude | msl bound lower : 5000 msl bound upper : 14000 |
| Environment | |
| Flight Conditions | IMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tracon : lax |
| Operator | common carrier : air carrier |
| Make Model Name | B757 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | Other Other |
| Flight Phase | descent : approach descent other |
| Route In Use | arrival other arrival star : star enroute airway : lax |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 250 flight time total : 11800 flight time type : 1250 |
| ASRS Report | 395411 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : instrument pilot : commercial |
| Events | |
| Anomaly | aircraft equipment problem : less severe other anomaly other |
| Independent Detector | aircraft equipment other aircraft equipment : unspecified other flight crewa |
| Resolutory Action | none taken : unable |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Aircraft |
| Air Traffic Incident | other |
Narrative:
During approach runway 25L lax, first officer noticed map shift on arrival over civet intersection. Only 1 DME was updating FMS, my DME was on raw data. I can only surmise that first officer DME locked on a DME near the lax area and that the signal was not accurate. The FMS DME was 2 mi different than the raw data ILS DME. Significant error only in the lax area. I've never noticed such a large shift in the few mins it took for this event to occur.
Original NASA ASRS Text
Title: B757 ACFT ON STAR AND DSCNT HAD MAP SHIFT WHICH RPTR CAPT ATTRIBUTES TO THE LAX DME. RPTR CLAIMS THAT HIS RAW DATA SHOWED ACCURATE DME, BUT THE FMS WAS 2 MI OFF.
Narrative: DURING APCH RWY 25L LAX, FO NOTICED MAP SHIFT ON ARR OVER CIVET INTXN. ONLY 1 DME WAS UPDATING FMS, MY DME WAS ON RAW DATA. I CAN ONLY SURMISE THAT FO DME LOCKED ON A DME NEAR THE LAX AREA AND THAT THE SIGNAL WAS NOT ACCURATE. THE FMS DME WAS 2 MI DIFFERENT THAN THE RAW DATA ILS DME. SIGNIFICANT ERROR ONLY IN THE LAX AREA. I'VE NEVER NOTICED SUCH A LARGE SHIFT IN THE FEW MINS IT TOOK FOR THIS EVENT TO OCCUR.
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.