What are displayed on the MFDs when the MFDs are in the CDU backup mode?

When the MFDs are in the CDU backup mode, they display advisories. This mode is designed to provide critical information to the pilot when traditional data sources are unavailable or have failed. The primary purpose of showing advisories is to ensure that the pilot remains informed about the operational status of the aircraft without overwhelming them with alerts that may not require immediate attention.

Advisories are essential for maintaining situational awareness, particularly during abnormal conditions, as they can guide the pilot in making informed decisions regarding flight safety and compliance with operational procedures. The display of these advisories in backup mode ensures that while some functionalities are limited, critical operational data still remain accessible to the pilot.