A great deal of risk/hazard identification is running through "what if" scenarios. Obviously, the big one is "what if an aircraft crashed?" but others include "what if the lights failed?" and "what if key staff left?" A tweet and associated webpage from the NBAA got me thinking about this scenario - "what if the NOTAM system went down?" Granted, the linked scenario is planned maintenance but it still requires consideration and maybe so does it's unplanned alternative scenario.
How would your aerodrome handle the NOTAM system being down? Do you have sufficient communication systems in place to ensure adequate flow of information to regular aerodrome users? Would you reschedule or abandon airside works? There are plenty of things to consider and the relative importance of each will vary between airports.
Perhaps NOTAM system vulnerabilities should make an appearance on your airport's risk register.