It is very alarming that the British Airways computer crash on Saturday 27th May 2017 shut down its entire operation. Apparently it was due to a power failure. That there was no back up power supply or UPS (Uninterruptible Power Supply) as it is called, is remarkable. That a major international transport system, with a world wide network of routes, can run its operation on a single, interconnected system technology without any backup system, demonstrates a serious lack of management responsibility. And, it has serious implications for the railway industry.
Normally a vital operation will have a some sort of back up or UPS to provide business continuity. But, consider this: if a system is vital and safety related, it needs to have a UPS. This will come into action when the main power system fails so that the operation keeps going. However, there is a trend nowadays that says, "If the UPS isn't available, the main system shouldn't be allowed to start up." And, "If the UPS fails, the main system must be shut down because it doesn't have a working backup." This is crazy. If this is your designer's philosophy, then you don't need a backup because it will eventually shut down your operation whenever it fails.
Railway signalling and train control systems are going the same way.