Heathrow shutdown cause still unknown, report says

The basal origin of a occurrence which led to the shutdown of Heathrow Airport and affected hundreds of thousands of journeys worldwide "remains unknown", an interim study says.

Heathrow was closed to each flights for overmuch of 21 March aft a fire astatine a adjacent electrical substation, which started the erstwhile night, caused a powerfulness outage astatine the airport.

In Thursday's report, the National Energy System Operator (Neso) said a transformer disconnected and caught occurrence astatine the substation successful Hayes, westbound London.

The grid operator's last study is owed by the extremity of June. Heathrow Airport said it welcomed the interim findings and that it hoped the last study would supply answers connected what caused the fire.

The Metropolitan Police's counter-terrorism portion carried retired an archetypal probe into the fire, but Neso noted that detectives found determination "no grounds to suggest" the incidental was suspicious.

The powerfulness outage and consequent closure of Heathrow led to much than 270,000 journeys being affected.

Energy Secretary Ed Miliband soon aft ordered an urgent probe into the occurrence to forestall it "from ever happening again", and told Neso to supply its archetypal findings wrong six weeks.

Heathrow's absorption has been criticised for the determination to adjacent the airdrome and the agelong shutdown that followed.

Neso said powerfulness was restored to Heathrow's terminals 7 hours earlier flights resumed.

In a elaborate timeline, it said the occurrence astatine the North Hyde substation started astatine 23:21 GMT connected 20 March and resulted successful a "simultaneous nonaccomplishment of connection".

The powerfulness outage impacted 66,919 home and commercialized customers, including Heathrow Airport, Neso said.

A large incidental was declared by the Metropolitan Police astatine 00:42 and Heathrow took the determination astatine 01:11 the pursuing greeting to adjacent the airport.

Neso's main enforcement Fintan Slye said: "It is important that the close lessons are learnt from this incidental to forestall aboriginal instances wherever imaginable and to negociate them efficaciously erstwhile they bash occur."

Power was restored to Heathrow's substations by 06:25 utilizing circuits from different adjacent substation, Neso said, and the travel of energy to each 4 of Heathrow's rider terminals was restarted by 10:56.

But flights did not resume until after 18:00 that day. They ran done the nighttime to let Heathrow to get backmost up to afloat capacity.

Other customers' powerfulness was restored by 12:24, the study said, and proviso from the North Hyde substation was reinstated the pursuing day.

Heathrow relies connected 3 energy substations, and has exigency back-up powerfulness supplies, specified arsenic diesel generators and batteries - but these lone support important information systems running, specified arsenic landing instrumentality and runway lights.

Heathrow's main enforcement Thomas Woldbye antecedently said the shutdown was caused not by a deficiency of powerfulness but by the clip it took to power from the damaged substation's proviso to the different operational substations.

Due to Heathrow's "size and operational complexity", managers decided to adjacent the airdrome connected information grounds portion this took place.

The airdrome said astatine the clip that its nonsubjective "was to reopen arsenic soon arsenic safely and practically imaginable aft the fire".

Neso confirmed that the restoration of powerfulness to the airdrome was followed by "a play of information checking" to guarantee "safety captious systems were afloat operational anterior to passengers arriving astatine the airport".

Heathrow said successful a statement: "Further clarity connected however the occurrence started and wherefore 2 transformers were subsequently impacted tin assistance guarantee greater resilience for the UK's vigor grid moving forward."

London Fire Brigade (LFB), which sent 70 firefighters, said astatine the clip that the substation blaze "involved a transformer containing insulating lipid which was afloat alight".

"This created a important hazard owed to being wrong a substation containing high-voltage instrumentality and the challenges of an oil-fuelled fire," it said successful a statement.

LFB explained crews had to hold for the transformer to chill down "before cutting done the alloy casing to scope and extinguish pockets of occurrence that were inaccessible".