Narrative:

In cruise flight at FL360; shortly after completing the descent and approach brief; we received a 'fuel quantity fault' alert. This was quickly followed by the fuel system reverting to manual and the display of a 'select fuel manual' alert. The synoptic page indicated the number 3 main tank fuel quantity had failed and was replaced with an amber x. The reversion to manual fuel management brought on all tank pumps. We also noticed the loss of prof [descent profile] indications; as well as the loss of numerous values in the FMC and on the speed tape. We ran the QRH for fuel quantity fault because it was the initial fault that began this series of events. The checklist directs the crew to calculate the fuel remaining in the affected tank by subtracting the fuel used from the departure fuel for the flight. With the dispatched MEL for #1 fuel flow; the fuel used on # 1 engine was blank and therefore there was no way to do this as directed. The only option to estimate the fuel in the tank was by referencing the other main tanks knowing the fuel should have been in balance prior to the fault. We were tank to engine on the fuel flow; so they should be relatively similar. Since it was referenced in the QRH; we checked the ufob on the init page and it was blank. This explained the loss of prof as the FMS had no ufob value; hence no aircraft gw to calculate speeds and profiles. Even after calculating the estimated onboard fuel and trying to initialize the ufob in the FMS; the FMS would not accept the value. This was because there was no fuel used indications for the FMS to use to update the fuel on board and ground weight as fuel was burned to provide accurate data for speed and decent calculations. Unable to get any profile information from the FMS; we reverted to manual flying of the descent using 3 to 1 planning and using the vvi and remaining time to turn points to gauge our progress. Due to lack of approach speed info from the FMS; we used the QRH approach tables to calculate the approach speed. To confirm the value was accurate; we would be referencing the aoa as we carefully slowed to approach speed. As we approached top of descent; center slowed us down to 250 knots. We began our descent as soon as cleared and were looking good on the STAR profile. However; center leveled us off for traffic at FL190 and kept us there for some time. By the time center gave us clearance to continue the descent; we could not make the subsequent restrictions. We informed center and they acknowledged; telling us to rejoin the profile as soon as possible from above. We rejoined the profile at about 6000 feet. Descending through about 7000 feet; the #3 main tank indication returned to normal and we got the FMS information back. We found that our fuel estimate was very close and the approach speed was as well. We flew a visual approach and landed uneventfully. The QRH procedure for fuel quantity fault should be amended to include the scenario of having a fuel flow inoperative. It creates numerous issues for the descent and landing. We had enough time in cruise to evaluate the situation before beginning descent; but if someone had this problem on descent on a clear day with little fuel; a crew could be pressed by their fuel state before having enough time to diagnose something they've never encountered. A clear definition of this specific situation in the QRH could be critical.the flight landed in VFR conditions at the diversion airport and taxied to the gate without further incident. The primary cause of this event was an aircraft component malfunction that resulted in an uncontrollable cabin altitude.

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Original NASA ASRS Text

Title: MD11 First Officer reported being dispatched with an MEL for number one fuel flow inoperative. Approaching Top of Descent the number three tank fuel quantity failed rendering many FMC calculations. QRH procedures were not accomplished due to the lack of any fuel numbers from the FMC. Numbers returned to normal during descent.

Narrative: In cruise flight at FL360; shortly after completing the descent and approach brief; we received a 'Fuel Quantity Fault' alert. This was quickly followed by the fuel system reverting to manual and the display of a 'Select Fuel Manual' alert. The synoptic page indicated the number 3 main tank fuel quantity had failed and was replaced with an amber x. The reversion to manual fuel management brought on all tank pumps. We also noticed the loss of prof [descent profile] indications; as well as the loss of numerous values in the FMC and on the speed tape. We ran the QRH for fuel quantity fault because it was the initial fault that began this series of events. The checklist directs the crew to calculate the fuel remaining in the affected tank by subtracting the fuel used from the departure fuel for the flight. With the dispatched MEL for #1 Fuel Flow; the fuel used on # 1 engine was blank and therefore there was no way to do this as directed. The only option to estimate the fuel in the tank was by referencing the other main tanks knowing the fuel should have been in balance prior to the fault. We were tank to engine on the fuel flow; so they should be relatively similar. Since it was referenced in the QRH; we checked the UFOB on the init page and it was blank. This explained the loss of prof as the FMS had no UFOB value; hence no aircraft GW to calculate speeds and profiles. Even after calculating the estimated onboard fuel and trying to initialize the UFOB in the FMS; the FMS would not accept the value. This was because there was no fuel used indications for the FMS to use to update the Fuel on Board and Ground Weight as fuel was burned to provide accurate data for speed and decent calculations. Unable to get any profile information from the FMS; we reverted to manual flying of the descent using 3 to 1 planning and using the VVI and remaining time to turn points to gauge our progress. Due to lack of approach speed info from the FMS; we used the QRH approach tables to calculate the approach speed. To confirm the value was accurate; we would be referencing the AOA as we carefully slowed to approach speed. As we approached top of descent; center slowed us down to 250 knots. We began our descent as soon as cleared and were looking good on the STAR profile. However; center leveled us off for traffic at FL190 and kept us there for some time. By the time center gave us clearance to continue the descent; we could not make the subsequent restrictions. We informed center and they acknowledged; telling us to rejoin the profile as soon as possible from above. We rejoined the profile at about 6000 feet. Descending through about 7000 feet; the #3 main tank indication returned to normal and we got the FMS information back. We found that our fuel estimate was very close and the approach speed was as well. We flew a visual approach and landed uneventfully. The QRH procedure for Fuel Quantity Fault should be amended to include the scenario of having a fuel flow inoperative. It creates numerous issues for the descent and landing. We had enough time in cruise to evaluate the situation before beginning descent; but if someone had this problem on descent on a clear day with little fuel; a crew could be pressed by their fuel state before having enough time to diagnose something they've never encountered. A clear definition of this specific situation in the QRH could be critical.The flight landed in VFR conditions at the diversion airport and taxied to the gate without further incident. The primary cause of this event was an aircraft component malfunction that resulted in an uncontrollable cabin altitude.

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.