Heathrow Airport has been shut all day after an "unprecedented" fire hit a nearby substation. Counter-terrorism police are leading the investigation into the blaze, with thousands of people affected by plane cancellations and power cuts. 
  
On the Sky News Daily, Rob Powell talks to The Independent’s travel writer Simon Calder about how airports prepare for an emergency. He also talks to Sky's data and forensic correspondent Tom Cheshire about how one fire closed Europe's biggest airport and what lessons can be learned. 

Podcast producer: Natalie Ktena
Editor: Philly Beaumont