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37000 Feet | Browse and search NASA's Aviation Safety Reporting System |
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Air carrier medium large transport strays off airway as FMC goes to a dead reckoning mode. Alert controller inquires about deviation.
| Attributes | |
| ACN | 156414 |
| Time | |
| Date | 199009 |
| Day | Wed |
| Local Time Of Day | 1801 To 2400 |
| Place | |
| Locale Reference | atc facility : mol |
| State Reference | VA |
| Altitude | msl bound lower : 35000 msl bound upper : 35000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zdc |
| Operator | common carrier : air carrier |
| Make Model Name | Medium Large Transport, Low Wing, 2 Turbojet Eng |
| Navigation In Use | Other Other |
| Flight Phase | cruise other |
| Route In Use | enroute airway : zdc |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 130 flight time total : 10000 flight time type : 450 |
| ASRS Report | 156414 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : commercial pilot : flight engineer pilot : instrument |
| Experience | flight time last 90 days : 60 flight time total : 2600 flight time type : 60 |
| ASRS Report | 156248 |
| Events | |
| Anomaly | aircraft equipment problem : less severe non adherence : clearance other spatial deviation |
| Independent Detector | other controllera other flight crewa |
| Resolutory Action | flight crew : returned to intended course or assigned course |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Ambiguous |
| Air Traffic Incident | Pilot Deviation other |
Narrative:
We were navigating using the FMS 'map' mode on electronic instrument displays (glass cockpit). As we approached mol NAVAID, system annunciation showed 'D/right' (dead reckoning) indicating that we had lost navigation station updates to FMS ahrs (altitude heading reference system). About same time ATC called and asked us if we were showing on arwy because he showed us about 8 NM north of course. When we switched to 'arc' display to show navigation right information it too showed us 'off course'. Evidently FMS system was working with erroneous crosswind of 350/101. When we selected 'progress page' of FMS it showed no navaids in use, the system was 'lost'. We reset our present position (using NAVAID and DME) on FMS position page. FMS reestablished (and found) itself and we regained FMS navigation guidance. Even though we periodically crosschecked FMS navigation data. It caught us off our guard.
Original NASA ASRS Text
Title: ACR MLG STRAYS OFF AIRWAY AS FMC GOES TO A DEAD RECKONING MODE. ALERT CTLR INQUIRES ABOUT DEVIATION.
Narrative: WE WERE NAVIGATING USING THE FMS 'MAP' MODE ON ELECTRONIC INSTRUMENT DISPLAYS (GLASS COCKPIT). AS WE APCHED MOL NAVAID, SYS ANNUNCIATION SHOWED 'D/R' (DEAD RECKONING) INDICATING THAT WE HAD LOST NAV STATION UPDATES TO FMS AHRS (ALT HDG REFERENCE SYS). ABOUT SAME TIME ATC CALLED AND ASKED US IF WE WERE SHOWING ON ARWY BECAUSE HE SHOWED US ABOUT 8 NM N OF COURSE. WHEN WE SWITCHED TO 'ARC' DISPLAY TO SHOW NAV R INFO IT TOO SHOWED US 'OFF COURSE'. EVIDENTLY FMS SYS WAS WORKING WITH ERRONEOUS XWIND OF 350/101. WHEN WE SELECTED 'PROGRESS PAGE' OF FMS IT SHOWED NO NAVAIDS IN USE, THE SYS WAS 'LOST'. WE RESET OUR PRESENT POS (USING NAVAID AND DME) ON FMS POS PAGE. FMS REESTABLISHED (AND FOUND) ITSELF AND WE REGAINED FMS NAV GUIDANCE. EVEN THOUGH WE PERIODICALLY XCHKED FMS NAV DATA. IT CAUGHT US OFF OUR GUARD.
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.