A quarter-million passengers who were due to fly to, from or via Heathrow on Friday and over the weekend saw their travel plans wrecked. They now want answers about why, exactly, the airport closed for nearly 24 hours.

Heathrow has launched a review by an independent board member, former transport secretary Ruth Kelly.

The airport chairman, Lord Paul Deighton, said:”The Kelly Review will analyse all of the relevant material concerning the robustness and execution of Heathrow’s crisis management plans, the airport’s response during the incident and how the airport recovered the operation with the objective of identifying any improvements that could be made to our future resilience.”

In other words: could we do better next time?

But the government insists such a close-down “should be prevented from ever happening again”.

The energy secretary, Ed Miliband, has commissioned the independent National Energy System Operator “to urgently investigate the power outage incident” and “the UK’s energy resilience more broadly”.

The airport told airlines and passengers no flights would operate on Friday, though towards the end of the day 10 departures were permitted.

Thomas Woldbye, Heathrow’s chief executive, has come under attack for the airport’s handling of the incident.

The chief executive of the National Grid, John Pettigrew, told the Financial Times on Sunday that the airport could have kept going.

In response, a Heathrow airport spokesperson said: “Hundreds of critical systems across the airport were required to be safely powered down and then safely and systematically rebooted. Given Heathrow’s size and operational complexity, safely restarting operations after a disruption of this magnitude was a significant challenge.

“In line with our airline partners, our objective was to reopen as soon as safely and practically possible after the fire.”

Speaking to The Independent at the weekend, Thomas Woldbye insisted closing the airport was the only option.

“It’s not an easy decision,” Mr Woldbye said. “But it’s also not that difficult, because our primary concern is safety. And if we can see we cannot safely operate the airfield, and guarantee passenger safety and colleagues and aircraft, then the decision to close is not that difficult.

“You can always look back and say, ‘Was that the right decision?’

“When I look at it now, I don’t think we had much choice than to say, hold on, we’ve lost so much power.

“Any big airport has thousands of systems. you have baggage systems, you have fuel systems, you have safety systems – ventilation, fire systems. They all have to be retested. They all have to be seen to be running for a period before you can legally open.

“People tend to forget that we are highly regulated. We have to have all of our systems in prudent operation and that just takes time. And you can’t start them all at one time because then you get a power surge and you have to start all over because all the fuses blow. So you have to do it step-by-step.”

“Of course we will have a proper de-brief on this, and we will look at: are there things we can do?

“There is always a call on the level of contingency that you have.

“I compare it a little bit to a highway. You have lanes, you have an emergency lane on your highway that will take care of 95 per cent of all your contingencies.

“But if someone takes out the entire highway, you don’t have any more lanes to do good with. And that’s the same here.”

The Heathrow CEO described the substation fire as “unprecedented”, saying: “I don’t know if you ever heard of a fire in a transformer station of this size in the UK? It’s not something that happens every day.

“We were reacting to the consequences of a transformer station that went down.

“We have to be able to trust the infrastructure around us. We were left to deal with the consequences.”

In other words: the airport was dealt a difficult hand and responded in the only way it could.

What, though, is Thomas Woldbye’s message to passengers?

“Our primary concern is safety and we will operate when it is safe. My message would be: it is 100 per cent safe to go through Heathrow. That’s how we operate. That’s why we closed down: because it was not.

“When we operate, we operate with the right margin of resilience, and with the right level of safety. That’s our first priority. The next, of course, is the convenience for our passengers.”