PA system - for making announcements to the passengers - used to brief passengers on emergency equipment and procedures, used in emergencies to tell the passengers what to do, used to tell them the meal service is about to start ..... etc etc

 

A PA system is required in an aeroplane with a maximum approved passenger seating configuration of more than 19.

 

The PA should be audible and intelligible at all passenger seats, toilets and cabin crew seats and work stations.