The activation of BUSS is provided to both PFDs when _____________.

The activation of BUSS is provided to both PFDs when _____________.

• A. the flight crew uses the emergency BUSS switch
• B. the BUSS is activated automatically during power-up
• C. the flight crew selects the BKUP SPD/ALT pushbutton on its associated side
• D. a fault in the PFDs alone activates BUSS

Answer: (C)

The key idea here is how backup power and data are shared between both PFDs. On the A320, there is a backup path to keep the PFDs powered and to provide backup speed/altitude information when needed. Selecting the BKUP SPD/ALT pushbutton on the side you’re working from closes a path that energizes the shared BUSS (the backup power bus) and feeds it to both PFDs. This ensures both displays stay powered and show the backup data simultaneously, which is crucial if normal sources fail and you need a reliable, single source of backup information on both screens. This differs from an emergency BUSS switch, which is a separate, other-purpose action, and from automatic power-up during power-on or a fault in a single PFD, which wouldn’t by itself deliver this coordinated BUSS activation to both displays.

The key idea here is how backup power and data are shared between both PFDs. On the A320, there is a backup path to keep the PFDs powered and to provide backup speed/altitude information when needed. Selecting the BKUP SPD/ALT pushbutton on the side you’re working from closes a path that energizes the shared BUSS (the backup power bus) and feeds it to both PFDs. This ensures both displays stay powered and show the backup data simultaneously, which is crucial if normal sources fail and you need a reliable, single source of backup information on both screens.

This differs from an emergency BUSS switch, which is a separate, other-purpose action, and from automatic power-up during power-on or a fault in a single PFD, which wouldn’t by itself deliver this coordinated BUSS activation to both displays.