On the ground, which switch activates the fresh air blower?

The correct answer is the landing gear weight-on-wheels switch. This switch is designed to ensure that certain aircraft systems only activate when the aircraft is on the ground, providing safety and functionality tailored to the conditions of ground operations.

When the landing gear is in contact with the ground, the weight-on-wheels switch closes, which can activate various systems, including the fresh air blower. This is crucial for ensuring that the passengers and crew have a comfortable environment during ground operations without unnecessary power consumption when airborne.

Other options do not specifically relate to activating the fresh air blower during ground operations. The power switch generally controls the overall power to the aircraft systems but does not directly activate individual components like the fresh air blower. The air conditioning switch is more focused on controlling the cabin's air conditioning system rather than the fresh air blower itself. The defog switch is intended for clearing the windows and windshields by directing airflow and heat, which is separate from the function of the fresh air blower on the ground.