Depending on whose fault it eventually turns out to be, this was a power cut in just the wrong – or right – place. As Britain’s biggest airport, Europe’s main gateway to the Americas, and the apple of Rachel Reeves’s eye for growth, Heathrow’s shutdown gave a supersized significance to a substation fire.

Some were quickly out of the blocks to question the creaking state of national infrastructure. Where were the back-up systems – or indeed the further failsafes when the back-ups went up in smoke?

Should Heathrow be better prepared, given the critical importance of the hub airport – not least to the 250,000 or so international travellers who were expecting to fly in or out on Friday?

Did National Grid, struggling to keep up with the burgeoning demand in developing west London for electricity capacity, have questions to answer about a transformer bursting into flames?

Or was it, as the supplier refused to rule out – despite assertions from the Met police that there was “no indication” – foul play? Plenty of online speculation quickly asserted that the culprit was surely one Vladimir Putin, and Moscow may be as happy to be believed culpable as National Grid would be pleased to identify an external culprit.

While counter-terrorism detectives are investigating if anyone was directly responsible, others are calling for an inquiry into just what contingency plans Heathrow had available and what it could do about it. It is not a good look for an airport demanding a third runway to abruptly have no planes on its existing two.

The shutdown has thrown airlines around the world into disarray and will be leaving many people facing difficult, disrupted, expensive days. Potentially, for some it could be even longer – Heathrow serves 230 international destinations, but not all daily. It is also a hub where long-haul and short-haul passengers connect, with time-sensitive cargo in many planes’ holds.

Analysts have already calculated that travel insurers face a bill in the tens of millions; while airlines, which will not be liable for compensation claims but still will have to accommodate or reroute passengers, will probably count higher losses.

The latest incident could have been much worse: a saboteur aiming for maximum disruption might have timed it for the morning peak, with Heathrow’s four terminals crammed with passengers and its taxiways and gates primed with planes, rather than cutting the power off after the nightly closure.

Heathrow was able to turn back or divert 120 long-haul flights from Asia, Australia and the west coast of America long before arrival, rather than allowing a swarm of planes to circle over London in the morning.

Nonetheless, Sir David Omand, the former head of GCHQ, said that having a day-long closure was “a national embarrassment. It shouldn’t have happened.”

Willie Walsh, who was long a critic of the airport when he was the boss of British Airways and its owner IAG, and who is now head of the global airlines body, the International Air Transport Association, denounced “another case of Heathrow letting down travellers … a clear planning failure by the airport”.

Aviation has history with unexpected eventualities; some may recall even angrier BA passengers stranded in their thousands at Heathrow in 2017, when someone pulled out the wrong computer’s plug at the airline’s HQ.

But questions over the resilience of infrastructure are valid – now spanning not just maintenance of ageing assets, or security from potential attack, but also increasingly unpredictable extremes of weather as the climate crisis worsens.

Across transport, from railways to runways, there are raging debates about how much to invest in something deemed highly resilient, if you own it, or “gold-plated”, if you’re paying to access it.

Energy experts say UK power networks have a certain amount of redundancy, or spare capacity – but a guaranteed backup for something the size of Heathrow, a small city’s worth of power, also comes at a price that may outstrip any stoppage costs.

As it was, Heathrow’s power was reconnected by early Friday afternoon, although the time needed to ensure the workaround was reliable, durable and safe for thousands of passenger planes kept most flights grounded.

When it fully reopens, disruption will persist, and countless planes, crew and passengers of all nationalities will not be where they hoped to be for some time, and at some cost. Industry and parliamentary inquiries into winter resilience followed Heathrow’s last closure, from snow in 2010.

But perhaps the fact that a fire described as “apocalyptic” in the night was virtually extinguished by daylight by London’s firefighters; that power was restored before breakfast to most of the 67,000 homes also reliant on the North Hyde substation; and that all that occurred without casualty in the ground or air, also shows a certain resilience worth noting.