Which type of fuel is primarily accounted for unexpected changes during a flight?

The concept of contingency fuel is crucial in flight planning and mass and balance considerations. Contingency fuel is specifically allocated to manage unexpected situations or changes that may occur during a flight, such as unplanned weather diversions, altitude changes, and other operational deviations. By incorporating this fuel into the flight plan, pilots and operators ensure that there is a buffer to account for unforeseen circumstances that could otherwise jeopardize the safety and efficiency of the flight.

In contrast, trip fuel refers to the amount of fuel required to fly from the departure airport to the destination under normal circumstances, while diversion fuel is designated for rerouting to an alternate airport if needed. Final reserve fuel is a legally required amount of fuel that must be retained at the end of a flight, ensuring that an aircraft can land safely if necessary. Each of these types of fuel serves critical roles in overall fuel management, but it is the contingency fuel that explicitly addresses unexpected changes during the flight.