What must always be done prior to fueling an aircraft?

The requirement to bond the fuel supply to the aircraft before fueling is a critical safety measure in aviation. Bonding involves using a conductive connection to equalize the electrical potential between the fueling equipment and the aircraft. This process helps to prevent static electricity buildup, which can generate sparks and pose a significant fire hazard during fueling operations. By ensuring that both the aircraft and the fuel supply are at the same electrical potential, this practice aims to minimize the risk of ignition sources in an area where flammable vapors are present.

In contrast, disconnecting the aircraft battery is not universally required as a precaution before fueling and could lead to unnecessary disruptions in aircraft systems. Starting the aircraft engines before fueling would also be unsafe and counterproductive, as engines should be off during this operation to minimize risks. Finally, while removing passenger belongings is a good practice for ensuring safety and security, it is not a specific requirement for the fueling process itself. Therefore, bonding the fuel supply to the aircraft is the correct procedure to follow prior to fueling, emphasizing safety in the potentially hazardous environment surrounding fuel operations.