What is the minimum fuel level requirement for the main tanks before takeoff?

The minimum fuel level requirement for the main tanks before takeoff is established to ensure sufficient fuel is available for the flight, considering both planned operations and any potential contingencies during the flight. A half-full tank ensures that the aircraft has an adequate reserve to handle unforeseen circumstances, such as the need for a go-around or diverting to an alternate airport, in addition to the demands of the flight itself.

This requirement aligns with safety practices that prioritize having enough fuel for various phases of the flight and helps prevent situations that might arise if fuel levels are lower than optimal, such as fuel starvation or running out of fuel prematurely. Consistent adherence to this guideline is crucial for maintaining safety margins in operations.