What role does the FMS button have on the Reversion Panel?

The FMS (Flight Management System) button on the Reversion Panel is crucial for managing flight plan data input. It facilitates the pilot's ability to input, modify, and retrieve flight plan information from the FMS during flight operations. In conditions where primary flight displays are unavailable or compromised, the Reversion Panel allows pilots to maintain situational awareness and operational control by accessing essential flight management functions, including waypoints, routes, and other crucial navigational data. This ability is vital for ensuring safe navigation and adherence to the planned flight path, especially in challenging scenarios.

In contrast, the other options pertain to functions that are not directly related to the operation of the FMS through the Reversion Panel. Emergency landing procedures and autopilot modes are distinct functionalities, while fuel flow control is typically managed separately from the flight management system, focusing more on engine performance and fuel management aspects rather than navigation data input.