Narrative:

After initially powering up aircraft; the IRS (inertia reference system) position was blank. After aligning the irus; I checked the status of left/right irus and noted that the display page below was blank; no GPS status displayed. Maintenance was called and the GPS system was eventually meled under 34-xx-xx with ancillary mels for terrain awareness and warning system 34-xx-X/X and clocks 31-xx-X. We found out from maintenance that the aircraft had been updated the night before.in flight; several items were noted in FMC operation that were not functioning: takeoff reference page 1/2 no intersection - - - / - - -; MCP altitude intv function inoperative; N1 did not set climb [mode] at cruise altitude; the abeam prompt did not display on the legs page with a route amendment. These were the items that we noted.at the destination; maintenance was called to address the issues. Aircraft was removed from service. Last word received before going to another aircraft was the mmrs (multimode receivers) were sending bad data to the FMC and that caused the errors. If this can occur; my question is. Should the GPS MEL 34-xx-xx also address the potential FMC issues in the MEL procedure?separate issue same aircraft: we discovered potable water system did not work in flight (no water in sinks/coffee makers) and that the toilets flushed with vacuum only (no fluid). Hand sanitizer was placed in the lavatories and the flight attendants used canned water to keep the toilets sanitary inflight. I notified dispatch of the issue and they concurred to continue to destination. I was also notified by dispatch; as I already thought; the issue with the toilet fluid was a separate problem from the potable water issue (i.e. Separate systems for the fluid). Maintenance at the destination stated that the toilet uses the water from the potable system and that this was the reason for no fluid and the vacuum flush only. What is the correct answer? If it uses water from the potable system; I think that most aviators misunderstand the system.suggestions: need to possibly expand the GPS MEL to include the FMC; if the mmrs sending erroneous data to the FMC was the issue. Need to clarify to operations; if indeed; the potable water system supplies fluid to the toilet system.

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Original NASA ASRS Text

Title: B737-700 Captain reported having several FMC malfunctions and questioned whether the GPS MEL used in this event fully covered all the FMC issues encountered during this flight.

Narrative: After initially powering up aircraft; the IRS (Inertia Reference System) position was blank. After aligning the IRUs; I checked the status of L/R IRUs and noted that the display page below was blank; no GPS status displayed. Maintenance was called and the GPS system was eventually MELed under 34-XX-XX with ancillary MELs for Terrain Awareness and Warning System 34-XX-X/X and Clocks 31-XX-X. We found out from Maintenance that the aircraft had been updated the night before.In flight; several items were noted in FMC operation that were not functioning: Takeoff Reference Page 1/2 no INTERSECTION - - - / - - -; MCP ALT INTV function Inoperative; N1 did not set CLB [mode] at cruise altitude; the ABEAM prompt did not display on the LEGS page with a route amendment. These were the items that we noted.At the destination; Maintenance was called to address the issues. Aircraft was removed from service. Last word received before going to another aircraft was the MMRs (Multimode Receivers) were sending bad data to the FMC and that caused the errors. If this can occur; my question is. Should the GPS MEL 34-XX-XX also address the potential FMC issues in the MEL procedure?Separate issue same aircraft: We discovered Potable Water system did not work in flight (no water in sinks/coffee makers) and that the toilets flushed with vacuum only (no fluid). Hand sanitizer was placed in the lavatories and the Flight Attendants used canned water to keep the toilets sanitary inflight. I notified Dispatch of the issue and they concurred to continue to destination. I was also notified by Dispatch; as I already thought; the issue with the toilet fluid was a separate problem from the potable water issue (i.e. separate systems for the fluid). Maintenance at the destination stated that the toilet uses the water from the potable system and that this was the reason for no fluid and the vacuum flush only. What is the correct answer? If it uses water from the potable system; I think that most aviators misunderstand the system.Suggestions: Need to possibly expand the GPS MEL to include the FMC; if the MMRs sending erroneous data to the FMC was the issue. Need to clarify to operations; if indeed; the potable water system supplies fluid to the toilet system.

Data retrieved from NASA's ASRS site 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.