What must an aircraft have in terms of usable fuel before takeoff?

The requirement for an aircraft to have enough usable fuel before takeoff is that it must be capable of completing the flight to the final landing point while also maintaining an adequate reserve. This is crucial for ensuring the safety of the flight, as it accounts for variations in weather, potential diversions, and any unforeseen circumstances that may arise during flight. The policy is generally in place to ensure that pilots are not only prepared for their intended destination but also have enough fuel to safely manage a potential go-around or to reach an alternative airport if needed.

Meeting this fuel requirement safeguards against situations where running low on fuel could lead to critical emergencies, making it essential for all flights to adhere to the principle of having sufficient fuel reserves in addition to what is needed for the planned journey. The minimum fuel requirements are typically defined by aviation regulations and standards.