The chief executive of the National Grid has confirmed power was available to keep Heathrow open throughout Friday’s shutdown.
In an interview with the Financial Times, John Pettigrew said the fire that knocked out a substation was a “unique event”, but that two other substations remained operational and capable of powering the airport in west London.
Heathrow chief executive Thomas Woldbye had said on Friday that the shutdown was not caused by a lack of power, but was due to the time it took to switch from the damaged substation to the other two.
The airport is under pressure from airlines to explain why flights were suspended for 18 hours after the fire in the early hours of Friday morning.
The fire started in a transformer within the electrical substation in Hayes north of Heathrow around midnight.
The airport has emergency back-up power supplies, which use diesel generators and batteries, but these only keep crucial safety systems running, such as landing equipment and runway lights.
A separate biomass power generator also provides heat and electricity to Terminal Two.
However, the National Grid is the main source of power for Heathrow.
Mr Pettigrew told the Financial Times said he couldn’t remember a transformer failing to such an extent in his 30-year career in the industry.
“Losing a substation is a unique event but there were two others available. That is a level of resilience.”
A Heathrow spokeswoman said that Mr Pettigrew’s comments “confirms that this was an unprecedented incident and that it would not have been possible for Heathrow to operate uninterrupted.
“Hundreds of critical systems across the airport were required to be safely powered down and then safely and systematically rebooted,” she said.
“Given Heathrow’s size and operational complexity, safely restarting operations after a disruption of this magnitude was a significant challenge.”
On Friday, Heathrow managers decided to close the airport on the grounds of safety while they switched to the alternative National Grid supplies.
Mr Woldbye told the BBC the delay to reopening was due to the need to “reallocate” the power supply – “closing down and restarting systems which takes a long time.”
He said there were a “number of systems we have to shut down and then bring them back up and ensure they are safe.”
“It’s fuelling systems, its bridges, it’s escalators, all of these systems have to be brought back up, tested to ensure they are safe.”
He added that there were risks “of certain sizes we cannot guard ourselves against 100% and this is one of them.”
However the duration of the shutdown has infuriated airlines.
Willie Walsh, the former British Airways boss and head of the airline organisation IATA said it was a “clear planning failure by the airport” and the systems and procedures for handling power failures are now under the spotlight.
The government’s ordered a six-week investigation into the shutdown, led by the National Energy System Operator.
Mr Woldbye, who attracted criticism for claiming the airport had “come back quite fast”, said he was “happy” to answer to the prime minister.
