What key factor must be considered when calculating fuel requirements?

The duration of the flight and the expected fuel burn rate are essential components when calculating fuel requirements for a flight. Understanding how long the flight will take and how much fuel the aircraft consumes over that duration allows pilots to determine the amount of fuel needed for a safe flight. This calculation ensures that the aircraft has enough fuel not only to reach its destination but also to account for any unexpected circumstances, such as diversions or delays.

While other factors like the total number of passengers and weather conditions may influence other aspects of flight planning, they do not directly impact the fundamental calculation of how much fuel is required for propulsion. The color and design of the aircraft are irrelevant with respect to fuel requirements, focusing instead on operational performance characteristics and efficiencies. Hence, the accurate assessment of duration and consumption rate is the most relevant factor for ensuring safety and compliance with regulations regarding minimum fuel thresholds.