What do double dashes displayed over the last two digits of the fuel on board (FOB) indication mean?

The display of double dashes over the last two digits of the fuel on board (FOB) indication signifies that while the fuel quantity indication system is still functioning, the information provided is not accurate. This situation typically occurs due to discrepancies in the fuel measurement system, often resulting from issues such as sensor malfunctions or configuration errors.

When double dashes are shown, it informs the pilots that they cannot rely on that specific fuel data for flight planning and operational decision-making. This understanding is crucial for maintaining safety and ensures that alternate methods of verifying fuel quantity, such as cross-checking with other instruments or fuel records, become necessary until the issue is resolved.

Other options involve different issues related to fuel management. However, they do not address the scenario of inaccurate but operational indications represented by the double dashes specifically.