What should the display reversion controller be switched to during a PFD/MFD failure?

When there is a failure of the Primary Flight Display (PFD) or Multi-Function Display (MFD), the display reversion controller should be switched to REV mode. This is the mode specifically designed to provide redundancy in the display of critical flight information.

In REV mode, the system routes the necessary information to the displays that are still operational, thereby ensuring that the pilot retains access to essential flight data. This reversion is crucial for maintaining safe operation when one of the primary displays malfunctions. The other modes, such as Normal, Backup, or Test mode, do not serve the immediate need for displaying essential flight data in a failure scenario in the same way REV mode does. Normal mode does not address failure situations, Backup mode typically does not provide the totality of information needed during a display failure, and Test mode is used for system checks rather than operational use.