What are 'auto-emergency' brakes?

Many locos used in steep ghat sections also have an 'auto-emergency' ('AE' or 'AEB') brake system, which consists of an additional safety circuit which monitors the speed and applies the brakes to slow down or halt the locomotive if the speed rises above a certain threshold (sometimes 25km/h or so, but this varies with the route and the working rules in effect). There isn't a separate set of brakes, but rather, the loco brakes are applied independent of the driver's control when the system is armed. The system is armed by using a key that the driver then hands to the guard. If the brakes trigger automatically, the key has to be retrieved from the guard and used again to get the train going (and a lot of paperwork has to be filed as well!). AE brakes are used especially on the WDM-2/WDM-2C/WDG-2 locos from Gooty that work the Braganza ghat. The AE brake system is armed when the locos are going in the downhill direction; its use is mandatory as there are no other safety features such ...  more