B737-700
Flight Crew Last 90 Days 390
Confusion; Human-Machine Interface; Troubleshooting; Training / Qualification; Time Pressure
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural MEL / CDL
General Flight Cancelled / Delayed; General Maintenance Action
Aircraft; Chart Or Publication; Procedure
During preflight operations; after refueling; the Captain noticed that the fuel quantity in the FMC was still at the inbound fuel state (the FMC fuel quantity was not automatically updating). Maintenance issued MEL 34-36-02; which essentially rendered our FMCs inoperative; leaving us to operate at a lower automation level than desired. Everything else operated normally. The Captain advised after discussion with the Assistant Chief Pilot on Call and Dispatch; this was the correct MEL. As a result; we departed late.
During aircraft turn at the gate; I noticed that the FMC fuel total on the Progress page one was still reading 6.3 (our arrival fuel) and our gauges showed 13.3 (the correct amount). Also; at the 'fuel on board' location on the initial page showed only dashes. Maintenance came out and it appeared that something in the fuel reader was not powered. Basically the fuel total was not getting to the FMC. Beyond that everything worked normally. I could type in the fuel manually. In the -300 we could MEL the fuel summation unit and then fly the plane normally while typing in the current fuel periodically in the FMC. That was what I was expecting to happen in this case. However when I reviewed the MEL 34-36-02 (what Maintenance deferred it under); I was surprised. Apparently there is not fuel summation unit in the -700 so the MEL stated that both FMC were malfunctioning and not to be used. They said it was this or grounding the aircraft. I contacted Dispatch and the Chief Pilot on call because I was concerned about this. A recent pilot brief just stated the Company cannot afford to apply/approve the wrong MEL. In my opinion I had a malfunctioning input to the FMCs regarding only one parameter; the total fuel. The MEL was saying that we had two complete FMC failures. Dispatch reworded it and said the FMCs was not getting the correct information. Both wordings are technically correct. Since the plane was perfectly safe to fly and I could do so with the MEL restrictions; I had no problems with regards to safety. My biggest concern was the legal definitions. Since both Dispatch and the Chief both agreed that it was OK to go with this particular MEL I agreed with it. The reason for this report is to ask if this is indeed a correct way to apply the MEL in this case. On a side note; MEL 34-36-02 provides very little guidance. I would think there would be more information since it is basically saying that all the information in the FMC is considered bad. No VNAV; autothrottles only in certain autopilot modes; disregard all speed tape envelopes and flap speed indications. Use performance manual values for thrust settings and cruise altitudes or default to standard values in FOM. Side note: the -700 does not fly a VOR/LOC radial nearly as well as the -200's did. I also highly recommend adding an MEL for this condition. The FMC is set up to fly using manual fuel settings; why take away a fully automated -700 and turn it into a -200 when you don't have to. If the MEL was applied correctly just add an MEL for this condition so we don't lose all the capabilities of a fully automated -700.
A B737-700 crew noted that the fuel quantity value was not automatically entering the FMC and subsequently Maintenance MEL'ed the FMC for automated VNAV operation because performance data would be inaccurate.