What is the function of the Avionics Master buttons on the overhead panel?

What is the function of the Avionics Master buttons on the overhead panel?

• A. Disable avionics to prevent transients during APU start on the ground
• B. Connect avionics to emergency bus
• C. Allow disconnection of navigation and communication equipment, preventing undesirable voltage transients during APU starting on the ground
• D. Enable automatic power restoration after APU start

Answer: (C)

The Avionics Master switches are used to isolate the avionics from the electrical power buses to prevent voltage transients when starting the APU on the ground. By disconnecting the navigation and communication equipment from the buses, the sensitive avionics are protected from surges or spikes that can occur during APU start. Once the APU start is complete, these switches are re-enabled to restore normal power to the avionics. This isn’t about permanently disabling the avionics or tying them to the emergency bus, and it isn’t about automatic power restoration—the function is to provide a safe, temporary isolation during APU start.

The Avionics Master switches are used to isolate the avionics from the electrical power buses to prevent voltage transients when starting the APU on the ground. By disconnecting the navigation and communication equipment from the buses, the sensitive avionics are protected from surges or spikes that can occur during APU start. Once the APU start is complete, these switches are re-enabled to restore normal power to the avionics.

This isn’t about permanently disabling the avionics or tying them to the emergency bus, and it isn’t about automatic power restoration—the function is to provide a safe, temporary isolation during APU start.