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An air carrier B757 first officer reports that his FMC presented no usable information after being worked on by a mechanic in sjo.
| Attributes | |
| ACN | 351681 |
| Time | |
| Date | 199610 |
| Day | Thu |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | airport : sjo |
| State Reference | FO |
| Altitude | agl bound lower : 0 agl bound upper : 0 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tower : sjo |
| 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 | cruise other ground : preflight |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : cfi pilot : flight engineer pilot : atp |
| Experience | flight time last 90 days : 100 flight time total : 5500 flight time type : 700 |
| ASRS Report | 351861 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Events | |
| Anomaly | aircraft equipment problem : less severe |
| Independent Detector | aircraft equipment other aircraft equipment : unspecified other flight crewa |
| Resolutory Action | flight crew : overcame equipment problem |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Aircraft |
| Air Traffic Incident | other |
Narrative:
Initial reference units (irus) aligned on ground, faulty light in left initial reference unit. Mechanic called, who turned off left initial reference unit only, reset circuit breakers and realigned left initial reference unit. No information dropped out of FMC, so present position and route were not re-entered, just rechked. On takeoff, FMC information became garbage/unusable. HSI screen did not blank, but information was non sensical and any fixes we tried to enter did not appear or were at inappropriate distances. Completed flight to san salvador by reference to raw data. Was data drop caused by: 1) not re-entering present position? 2) not realigning all 3 initial reference units? (Only 1), or another reason? Note: this all done in presence/on instruction of mechanic under contract (not our mechanic). Presence of a mechanic led us to follow his suggestions rather than making our own decisions, but how well did he know the airplane?
Original NASA ASRS Text
Title: AN ACR B757 FO RPTS THAT HIS FMC PRESENTED NO USABLE INFO AFTER BEING WORKED ON BY A MECH IN SJO.
Narrative: INITIAL REF UNITS (IRUS) ALIGNED ON GND, FAULTY LIGHT IN L INITIAL REF UNIT. MECH CALLED, WHO TURNED OFF L INITIAL REF UNIT ONLY, RESET CIRCUIT BREAKERS AND REALIGNED L INITIAL REF UNIT. NO INFO DROPPED OUT OF FMC, SO PRESENT POS AND RTE WERE NOT RE-ENTERED, JUST RECHKED. ON TKOF, FMC INFO BECAME GARBAGE/UNUSABLE. HSI SCREEN DID NOT BLANK, BUT INFO WAS NON SENSICAL AND ANY FIXES WE TRIED TO ENTER DID NOT APPEAR OR WERE AT INAPPROPRIATE DISTANCES. COMPLETED FLT TO SAN SALVADOR BY REF TO RAW DATA. WAS DATA DROP CAUSED BY: 1) NOT RE-ENTERING PRESENT POS? 2) NOT REALIGNING ALL 3 INITIAL REF UNITS? (ONLY 1), OR ANOTHER REASON? NOTE: THIS ALL DONE IN PRESENCE/ON INSTRUCTION OF MECH UNDER CONTRACT (NOT OUR MECH). PRESENCE OF A MECH LED US TO FOLLOW HIS SUGGESTIONS RATHER THAN MAKING OUR OWN DECISIONS, BUT HOW WELL DID HE KNOW THE AIRPLANE?
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.