What is the purpose of the EMER/NORM button on the RTU panel?

The EMER/NORM button on the RTU (Radio Tuning Unit) panel serves the important function of allowing the user to bypass the audio control panel and create direct connections to the necessary communication systems. This is crucial during scenarios where immediate and reliable communication is required, such as emergencies, where relying on the normal routing through the audio control panel may not be feasible. By pressing this button, pilots can ensure that they have a direct connection to their communication means, which is vital for maintaining contact with air traffic control and other necessary parties during critical situations.

The other options describe different functionalities that are not associated with the EMER/NORM button specifically. For example, activating an emergency communication system is a broader action not limited to just this button, while switching frequencies and arming navigation systems involve separate procedures and controls.