Flights were suspended at Gatwick Airport following reports of drones flying close to the airfield. Here we look at the law surrounding drones.
What are the restrictions around flying drones near airports?
Earlier this year, new laws came into force which ban all drones from flying above 400ft and within 1km of airport boundaries.
Drone users who flout the height and airport boundary restrictions could face an unlimited fine, up to five years in prison, or both.
Research funded by the Department for Transport (DfT) found that a drone weighing 400g could smash a helicopter windscreen, and one weighing 2kg could critically damage an airliner's windscreen.
Are there any other laws to bear in mind?
Laws introduced to the Commons in May mean people flying drones which weigh 250g or more will have to register with the Civil Aviation Authority (CAA).
Drone pilots will be required to take an online safety test under the new legislation, with the requirements set to come into force in November next year.
In July, the DfT said it was considering introducing an age restriction, banning children from owning drones weighing at least 250g.
It also said it was considering giving police the power to issue on-the-spot fines of up to £300 for misuse and the ability to seize drones being used irresponsibly.
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Have there been any incidents at airports in the past?
According to the British Airline Pilots Association (Balpa), there were already 117 near misses between manned aircraft and drones up until November this year, compared to 93 for the whole of 2017.
This is not the first time an incident involving drones has been reported at London Gatwick.
In October, it was reported that a drone "put 130 lives at risk" after nearly hitting an aircraft approaching the airport over the summer.
According to the UK Airprox Board, the flying gadget passed directly over the right wing of the Airbus A319 as it was preparing to land at the West Sussex airport in July.
Also in October, a drone collided with a commercial aircraft as it was approaching to land in Canada.
There were six passengers and two crew on the aircraft and the drone connected with its wing, but fortunately it suffered only minor damage, allowing it to land safely at Jean Lesage International Airport in Quebec City.
How can people stay safe flying drones?
Balpa has urged people be aware of the rules before they take their drone out and about.
Dr Rob Hunter, head of flight safety, said: "Even two kilograms of metal and plastic, including the battery, hitting an aircraft windscreen or engine or a helicopter tail rotor, could be catastrophic.
"People who buy these devices need to make sure that they know the rules and stick to them, so they don't put anyone's life in danger.
"Pilots don't want to ruin anyone's fun but if you are going to use drones the message is clear: Know the laws or expect serious consequences.
"Before taking to the air have a really good think about where you are, keep your drone in sight, consider what aircraft might be flying about and keep clear - it is your responsibility."
The runway at Gatwick remains closed on Thursday morning following reports of drones flying close to the airport - despite briefly reopening overnight.
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What's happened at Gatwick?
Flights in and out of the airport were suspended at about 9pm on Wednesday after two drones were sighted near the airfield.
Gatwick announced that the runway had reopened at about 3am on Thursday - but just 45 minutes later it was shut again.
In a statement, the airport said: "Following reports of two drones flying over the Gatwick Airport airfield at around 9pm, the airfield was closed from 21.03 on Wednesday 19th December to 03.01 on Thursday 20th December.
"Unfortunately a further sighting of drones in the vicinity of the airport has forced the runway to be closed again from 03.45 as we investigate the sighting alongside Sussex Police.
"We will update when we have suitable reassurance that it is appropriate to reopen the runway."
Passengers faced delays to their travels on Wednesday night as some flights were unable to leave the tarmac while others were diverted to alternative airports.
Some people reported being left stuck on planes for several hours while they waited to find out what was going on.
Gatwick advised anyone flying from the airport, or collecting someone, to check the status of their flight.