Why is it important to ground both the aircraft and fuel truck during refueling?

Grounding both the aircraft and the fuel truck during refueling is primarily focused on reducing the risk of static electricity accumulation, which can lead to electrical shock hazards or even ignition of flammable vapors. When fuel is pumped into an aircraft, the fuel can generate static electricity due to the physical movement and friction between the fuel and the truck's dispensing equipment. If static discharge occurs, it could create a spark that ignites the flammable vapors present in the area.

By grounding both the aircraft and the fuel truck, any static electricity that builds up is safely dissipated to the ground, significantly lowering the risk of a fire or explosion during the refueling process. This safety measure is critical in ensuring a safe refueling operation, which often occurs in environments where flammable materials are present.

While safety regulations and practices (option A) do encompass grounding protocols, the core reasoning stems from the need to handle electrical hazards specifically associated with static electricity during fueling operations. Balancing the fuel (option C) and preventing fuel spillage (option D) are important considerations for operational efficiency and environmental safety, but they do not directly address the grounding issue related to electrical hazards.