Before applying power to an aircraft after aircrew egress, which system must be deactivated?

• A. Fuel pump
• B. Navigation lights
• C. Hydraulic system
• D. Weather/radar system

Answer: (D)

The main safety concern here is avoiding high-energy, radiating systems being energized when the crew is not present to monitor or respond to any faults. The weather radar transmitter is a high-power RF device with high-voltage components. If power is applied while the radar is still energized, it can pose a shock/ RF hazard to personnel and potentially cause interference or damage. Deactivating the weather/radar system before applying power ensures there’s no active radar energy or associated high-voltage circuitry entering the ground operations area.

Other systems listed do not present the same immediate hazard to personnel when power is applied on the ground. The fuel pump, while important to fuel delivery, does not emit hazardous energy in the same way the radar does. The hydraulic system and navigation lights aren’t hazards requiring deactivation for safety just when powering up after crew egress.