Gatwick airport, the UK’s second largest airport, was closed for most of Wednesday night and Thursday morning after it received reports of two drones flying nearby, reports The Guardian, quoted by the Verge.

 The airport initially had its flights suspended at 9PM on Wednesday evening after the drones were spotted, and although it briefly reopened at 3am, it was forced to close once more 45 minutes later after the drone flights resumed. As of 9:15AM, Thursday morning, flights to and from the airport remained suspended.

As well as preventing any flights from taking off, the suspension means that numerous inbound flights had to be diverted to other London-area airports including Luton, Heathrow and Stansted, while other flights were forced to land in Paris and Amsterdam. In total, 760 flights containing 110,000 passengers were due to either take off or land from Gatwick over the course of Thursday.

Responding to the incident, the UK’s Civil Aviation Authority said that “it is totally unacceptable to fly drones close to airports and anyone flouting the rules can face severe penalties including imprisonment.” Currently, the law states that flying within 1km (0.6 miles) of an airport is illegal in the UK without explicit permission, and if caught, the pilots of Gatwick’s drones could face up to five years in prison according to the Aviation Minister Baroness Sugg. Although drone users in the US have been required to register their drones since 2015, similar rules for UK owners aren’t due to come into effect until November 2019.

Due to the difficulty of catching the pilots, technical measures have been proposed to ensure flying a drone near an airport is not just illegal, but technically impossible. One airspace security company has suggested that a combination of radar, camera detection, radio frequency detection, and jamming technologies could be used by airports to shut down illegal drone flights. As well as equipping its drones with geofencing software that prevents them from being flown in restricted airspace, DJI has developed technology that lets it detect drones from as much as 10 miles away.

Such measures might become necessary thanks to the increasing numbers of drone incidents that airports are experiencing. Dedrone, a site that tracks drone incidents globally, recorded 13 incidents in November 2018 across the USA, Switzerland, Germany, Austria, New Zealand, and the UK.