Which vehicle is primarily used for aircraft fueling on the ramp?

The primary vehicle used for aircraft fueling on the ramp is the fuel truck. Fuel trucks are specifically designed to transport and dispense aviation fuel to aircraft, ensuring that they receive the necessary fuel types, whether it's jet fuel such as Jet A or aviation gasoline, depending on the specific requirements of the aircraft. These trucks are equipped with specialized pumps and safety mechanisms to handle flammable liquids safely and efficiently.

Service vans are typically used for various passenger services or cargo management, while tug vehicles are primarily employed to move aircraft around the ramp and to different locations, such as the terminal or hangars. Maintenance trucks are meant for performing scheduled or unscheduled maintenance on aircraft and other equipment, not for fueling. Thus, the fuel truck is the only vehicle designed specifically for the task of fueling aircraft, making it the correct answer for this question.