Drones are causing airport chaos - why can't we stop them?

For the second time in less than a month, suspected drone sightings have shut down a UK airport. On 8 January flights out of London Heathrow were suspended for over an hour. And between 19 and 21 December, more than 140,000 people at London Gatwick had their travel plans disrupted after drones were spotted above the airport. How can drones cause so much disruption? Airports operate on a just-in-time basis, with Heathrow moving a plane onto or off its runways every 45 seconds on average. A drone could interrupt this flow if planes have to reroute.