What does the TOTAL FUEL LBS indicator show if a single tank indicator is inoperative?

The TOTAL FUEL LBS indicator displays the overall fuel total available for the aircraft. When a single tank indicator is inoperative, the system compensates for this failure by estimating the fuel amount based on the remaining operational tank indicators. This allows the pilot to still have a reliable figure for the total fuel on board, rather than simply indicating a malfunction.

This capability is vital for flight operations, as it ensures that the pilot has access to necessary information even in case of instrument failure. The estimation helps promote situational awareness regarding fuel management without leaving the pilot in uncertainty about fuel levels.

Other options were incorrect; the indicator would not show a blank window or a series of dashes, as these would imply a more severe instrument failure, leaving the pilot without any usable information. An estimated fuel value is not presented under these conditions; rather, the system adapts to provide a total amount based on available data from functional indicators.