Management 101?

Seems totally unbelievable that there was no backup for the computer system which runs the national air traffic control centre and which failed last weekend effectively grounding all UK aircraft and causing chaos for some 120,000 would-be travellers.  I think I've mentioned before that I saw an essential aspect of management to be constantly asking "what if?" and trying to ensure that all the bases were covered. Clearly where computer failure would produce such a catastrophic situation you would surely have another independent system (or maybe more than one) running in parallel and ready to cut in and take over should the need arise?