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B737-700 flight crew loses the FMC during RNAV departure. Flight crew reverts to standard navigation and requests vectors.
| Attributes | |
| ACN | 688311 |
| Time | |
| Date | 200602 |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | atc facility : l30.tracon |
| State Reference | NV |
| Altitude | agl single value : 500 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tracon : l30.tracon |
| Operator | common carrier : air carrier |
| Make Model Name | B737-700 |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | other |
| Flight Phase | climbout : initial |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Experience | flight time last 90 days : 220 flight time type : 8000 |
| ASRS Report | 688311 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Events | |
| Anomaly | aircraft equipment problem : less severe |
| Independent Detector | aircraft equipment other aircraft equipment : fmc other flight crewa other flight crewb |
| Resolutory Action | controller : issued new clearance controller : provided flight assist flight crew : overcame equipment problem |
| Supplementary | |
| Problem Areas | Aircraft |
| Primary Problem | Aircraft |
Narrative:
Immediately after takeoff from las we were not able to engage LNAV at 500 ft AGL. At the gate; we had programmed and confirmed the shead 4 RNAV departure; but after takeoff the FMC display reverted to dashed cyan lines -- inactive route. The first officer was the PF and he used 'heading select' to steer to roppr. Without conventional navigation backup after rbell; I informed las departure control that our FMC had malfunctioned and that we would need headings to fly the departure. We also noticed that there was an amber 'landing altitude' flag now. I tried to line select the roppr waypoint and go direct but got an 'altitude constraint' message. I tried to delete the shead altitudes but the computer would not allow the operation. I also noted that the cruise altitude had dropped out. By now; we had been given a heading to shead intersection and a climb to FL190. I was able to line select shead and go direct to that waypoint. I reinserted the cruise altitude and at that point the FMC returned to normal operation. I cannot offer an explanation for what happened.
Original NASA ASRS Text
Title: B737-700 FLT CREW LOSES THE FMC DURING RNAV DEP. FLT CREW REVERTS TO STANDARD NAV AND REQUESTS VECTORS.
Narrative: IMMEDIATELY AFTER TKOF FROM LAS WE WERE NOT ABLE TO ENGAGE LNAV AT 500 FT AGL. AT THE GATE; WE HAD PROGRAMMED AND CONFIRMED THE SHEAD 4 RNAV DEP; BUT AFTER TKOF THE FMC DISPLAY REVERTED TO DASHED CYAN LINES -- INACTIVE RTE. THE FO WAS THE PF AND HE USED 'HDG SELECT' TO STEER TO ROPPR. WITHOUT CONVENTIONAL NAV BACKUP AFTER RBELL; I INFORMED LAS DEP CTL THAT OUR FMC HAD MALFUNCTIONED AND THAT WE WOULD NEED HDGS TO FLY THE DEP. WE ALSO NOTICED THAT THERE WAS AN AMBER 'LNDG ALT' FLAG NOW. I TRIED TO LINE SELECT THE ROPPR WAYPOINT AND GO DIRECT BUT GOT AN 'ALT CONSTRAINT' MESSAGE. I TRIED TO DELETE THE SHEAD ALTS BUT THE COMPUTER WOULD NOT ALLOW THE OP. I ALSO NOTED THAT THE CRUISE ALT HAD DROPPED OUT. BY NOW; WE HAD BEEN GIVEN A HDG TO SHEAD INTXN AND A CLB TO FL190. I WAS ABLE TO LINE SELECT SHEAD AND GO DIRECT TO THAT WAYPOINT. I REINSERTED THE CRUISE ALT AND AT THAT POINT THE FMC RETURNED TO NORMAL OP. I CANNOT OFFER AN EXPLANATION FOR WHAT HAPPENED.
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.