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B737 flight crew was informed of navigation error. Off-course was apparently the result of a map shift.
| Attributes | |
| ACN | 756079 |
| Time | |
| Date | 200710 |
| Place | |
| Locale Reference | airport : mmtj.airport |
| State Reference | FO |
| Altitude | msl single value : 35000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : mmzt.artcc |
| Operator | common carrier : air carrier |
| Make Model Name | B737 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | other |
| Flight Phase | cruise : level |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Experience | flight time last 90 days : 300 flight time type : 8000 |
| ASRS Report | 756079 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Experience | flight time last 90 days : 220 flight time type : 3480 |
| ASRS Report | 756080 |
| Events | |
| Anomaly | non adherence : clearance other spatial deviation |
| Independent Detector | other controllera |
| Resolutory Action | aircraft : equipment problem dissipated controller : issued new clearance flight crew : returned to intended or assigned course |
| Supplementary | |
| Problem Areas | Aircraft Flight Crew Human Performance |
| Primary Problem | Aircraft |
Narrative:
In cruise; LNAV/VNAV and autoplt engaged. Shortly after passing tij; headed south to mmsd; mzt center informs us we are 10 mi east of the airway. We checked GPS and both were off course. We made the proper correction. Flight continued uneventfully. Write-up in logbook made. Maintenance technician met the aircraft in mmsd. Maintenance control notified while still en route. Rare occasion when both GPS and FMC position shift. Callback conversation with reporter revealed the following information: the reporter stated that all cockpit indications were normal prior to the event. Reporter stated that during the flight; some FMS scratch pad messages may have been ignored and were deleted. Apparently 'nuisance' messages are common and often canceled. The FMC generated course line appeared normal; but shifted when the flight was cleared direct to the next fix. The manufacturer was consulted and contributes the anomaly to a map shift and believes it to be a one-time occurrence.
Original NASA ASRS Text
Title: B737 FLT CREW WAS INFORMED OF NAV ERROR. OFF-COURSE WAS APPARENTLY THE RESULT OF A MAP SHIFT.
Narrative: IN CRUISE; LNAV/VNAV AND AUTOPLT ENGAGED. SHORTLY AFTER PASSING TIJ; HEADED S TO MMSD; MZT CTR INFORMS US WE ARE 10 MI E OF THE AIRWAY. WE CHKED GPS AND BOTH WERE OFF COURSE. WE MADE THE PROPER CORRECTION. FLT CONTINUED UNEVENTFULLY. WRITE-UP IN LOGBOOK MADE. MAINT TECHNICIAN MET THE ACFT IN MMSD. MAINT CTL NOTIFIED WHILE STILL ENRTE. RARE OCCASION WHEN BOTH GPS AND FMC POS SHIFT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE REPORTER STATED THAT ALL COCKPIT INDICATIONS WERE NORMAL PRIOR TO THE EVENT. RPTR STATED THAT DURING THE FLT; SOME FMS SCRATCH PAD MESSAGES MAY HAVE BEEN IGNORED AND WERE DELETED. APPARENTLY 'NUISANCE' MESSAGES ARE COMMON AND OFTEN CANCELED. THE FMC GENERATED COURSE LINE APPEARED NORMAL; BUT SHIFTED WHEN THE FLT WAS CLEARED DIRECT TO THE NEXT FIX. THE MANUFACTURER WAS CONSULTED AND CONTRIBUTES THE ANOMALY TO A MAP SHIFT AND BELIEVES IT TO BE A ONE-TIME OCCURRENCE.
Data retrieved from NASA's ASRS site as of January 2009 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.