The recent air traffic control disruption at NATS due to a flight plan has made many headlines and details of the causes are now being made public. It looks like some unexpected data in the plan caused the primary and backup software to fail. Both the upcoming SCSC Working Group meetings on Data Safety and Complex Systems will discuss the incident. However we shouldn't forget that the whole arrangement of aircraft and crews, rosters and allowable hours contributed to the problems - highlighting an astonishingly fragile complex system (in fact a service). From a robustness perspective, there should have been contingencies at every level so that the knock-on effects were reduced. We await the formal reports into the matter but there are clear lessons already: expect the unexpected and have backups which are diverse in nature.