Heathrow and the limits of electrical redundancy

The Heathrow outage prompts a provisional explanation based on infrastructure and electrical failure, while reports about the airport's substations remain conflicting. A large transformer fire can damage equipment upstream and downstream, potentially disabling backup systems that remain connected to the fault. One suggested explanation is that successive terminal expansions acquired separate supplies without creating a system in which every surviving supply could serve the whole airport. Independent feeds and switchgear isolation would improve resilience, but a severe fault could still damage equipment near the point of demand. A phase-to-phase short is discussed as a possible failure mechanism, rather than an established finding about this incident. The engineering question is whether apparent redundancy remains usable after the fault it is meant to cover.