NATS Holdings Limited

A valid flight plan with an unusual combination of route attributes stopped automated processing in both the primary and secondary UK flight-plan systems on 28 August 2023. Safety was preserved by restricting traffic, but the fallback could handle only a small fraction of normal demand. The incident therefore tests a harder proposition than whether NATS restored a computer: whether an essential monopoly service can show that redundancy is genuinely independent, software changes preserve defensive controls, degraded operations remain useful, and the costs of failure do not disappear into airlines' and passengers' balance sheets.