While investigation into a prolonged electrical power outage to London Heathrow is continuing, UK transport minister Heidi Alexander has told the country’s parliament that back-up power systems did not fail and acted as intended.
A large fire broke out at an electrical substation – located about 4km northeast of the airport – around 23:30 on 20 March, and the impact prompted Heathrow’s closure about 5h later, at 04:30 on 21 March.
“What we know is that there was an unprecedented outage, and that it was not the result of a single point of failure on the electricity transmission or distribution system,” Alexander stated to parliament on 24 March.
Although the substation was forced out of service by the damage, it is one of three supply points to Heathrow, says Alexander, and the other two “continued supplying” power to Heathrow “throughout the incident”.
But the airport operator’s view, she says, was that the supply was “insufficient” to ensure safe and secure operation of all systems across the airport.
“It proceeded to reconfigure its internal electricity network to enable the resumption of full operations, utilising the other two external supply points,” she adds.
“That required hundreds of systems to be safely powered down, and then safely powered up, with extensive testing.”
Although back-up generators and uninterruptible power supplies ensured safety systems were maintained, Alexander says they were “never designed to support full operation of the whole airport”.
In response to a parliamentary question during the session, Alexander added: “I am told that the back-up power systems at Heathrow operated as they should have done during this incident – they did not fail.”
Restart of systems at Heathrow did not commence until around 14:30 on 21 March and confidence in their functioning eventually enabled the airport to begin allowing positioning flights around 18:00.
Restrictions on night flights were temporarily lifted in order to facilitate the repositioning of aircraft and restoration of services.
Preliminary indications from police, says Alexander, indicates the fire is not considered to have been suspicious – although, given the impact on Heathrow, counter-terrorism officers are continuing to investigate.
Some 1,300 flights were cancelled and around 200,000 passengers affected.
Alexander was asked whether she was confident about the set-up for UK airport power supplies, but replied that she was “not going to become an armchair electrical engineer”.
She highlights that the government has ordered a probe into the occurrence, and Heathrow’s operator has sought an independent review of its internal resilience.
“We will look at any and all the issues that this incident raises in those reviews,” she adds.
