What action should a controller take when a pilot reports loss of low frequency navigational capability?

In the scenario where a pilot reports a loss of low frequency navigational capability, the appropriate action for a controller is to notify other controllers and provide required assistance. This is crucial because the aircraft may require additional help navigating safely. By notifying other controllers, they can be made aware of the situation and assist in managing the airspace, ensuring that proper communication and coordination occur. This could involve providing updated flight instructions, tracking the aircraft's position, and giving necessary guidance to help the pilot operate safely.

While other options might seem relevant in certain contexts, they do not address the immediate need for safety and coordination among air traffic control. Guiding the aircraft visually is not always feasible or safe, depending on the situation, while changing routes or requesting additional pilot reports may not provide the immediate assistance and support needed during a loss of navigational capability. Therefore, the selected action emphasizes communication and collaboration within air traffic control, which is critical for maintaining safety in the airspace.