Connor An interim report into the power outage that shut Heathrow Airport will be published on Thursday.
The airport was closed to all flights until about 18:00 GMT on 21 March due to an "unprecedented" loss of power caused by a fire at a nearby electricity substation, which started the previous night.
More than 270,000 air passenger journeys were disrupted.
In the immediate aftermath of the fire, the National Energy System Operator (NESO) was ordered by Energy Secretary Ed Miliband to investigate what happened and provide its initial findings within six weeks.
The NESO North Hyde Review Interim Report will focus on "establishing the timeline and sequence of events of the outage".
It aims to "explain the roles and responsibilities of the key stakeholders involved, and outline areas of further investigation required to deliver the final report by the end of June 2025", NESO has said.
Last month, MPs were told Heathrow Airport had been warned about its power supply in the days before the incident.
