What action must a Dispatcher take if the cab signal apparatus fails en route in ABS territory?

When the cab signal apparatus fails en route in ABS (Automatic Block Signal) territory, the correct action for a Dispatcher is to notify the connecting dispatcher. This action is crucial because the failure of the cab signal system could lead to compromised safety and control over train movements. Notifying the connecting dispatcher ensures that they are aware of the situation, allowing them to coordinate and take appropriate measures to maintain safe operations, such as issuing updates or instructions to the train crew for any changes in signal control or movement authority.

This response is not only operationally sound but also emphasizes the interconnectivity and reliance on communication within the railway system to handle unexpected situations. Effective communication helps in managing risks and ensuring that all personnel involved in train operations are informed and can act accordingly.