When can a commander plan the usage of final reserve fuel on a commercial flight?

Final reserve fuel is specifically designated for emergency situations and is intended to ensure that an aircraft can land safely in the event of unforeseen circumstances. The regulations surrounding fuel reserves emphasize that final reserve fuel should not be part of the normal fuel planning process for a flight; it is a safety measure that should only be accessed when all other fuel options have been exhausted. This means that the commander must ensure that final reserve fuel is strictly preserved for emergencies where no other options are viable.

Planning to use final reserve fuel during a flight, even if contingencies seem favorable, undermines its purpose. The functioning of aviation safety systems relies on strict adherence to these protocols, thereby preventing any preemptive usage. The concept is that reserve fuel gives a buffer during emergencies, while all operational fuel should be planned efficiently without touching this critical safety reserve.

While the other options touch upon situations that may seem plausible, they do not align with the understanding that final reserve fuel must be safeguarded exclusively for emergencies. Consequently, final reserve fuel is not something that can be factored into standard flight planning under any routine circumstances.