Explainer: How serious is a drone collision with an aircraft?
Birds colliding with aircraft have long been a known threat but rogue drones are increasingly becoming a bigger cause of concern in aviation.
Airports across the UK have witnessed a growing number of near-misses, with 92 reported in 2017, according to the UK Airprox Board.
Bird strikes can be catastrophic for aircraft, especially if the engine is hit, though serious incidents are rare. What sort of impact would a drone have if it hit a plane?
How serious is a drone collision with aircraft?
Any collision with an object can be serious but there have been few tests to assess the actual damage that could be caused.
"It doesn't take much imagination to understand the likely consequences of 3kg of metal and plastic, including the lithium-polymer battery, hitting a helicopter windshield or, perhaps worse, the tail rotor at 100mph," government advice states.
Researchers at the University of Drayton recently carried out a test, by launching a 2.1-pound DJI Phantom 2 quadcopter at 238 mph towards the wing of a Mooney M20 aircraft and a fake bird that weights a similar amount made of gel.
The results showed that the drone tore open the edge of the wing and did not shatter on impact, and damaged its main spar, which is used to keep the wing stable.
"While the quadcopter broke apart, its energy and mass hung together to create significant damage to the wing," said Kevin Poormon, group leader for impact physics at the university.
"The bird did more apparent damage to the leading edge of the wing, but the Phantom penetrated deeper into the wing and damaged the main spar, which the bird did not do."
However, the drone used in this test is mid-range - at least one of the drones in the Gatwick incident is believed to be industrial, meaning it will be bigger and stronger.
How many near-misses have there been in the UK?
According to the UK Airprox Board, reports of near-misses have rose sharply in recent years.
From 2015 to 2017, the number has more than trebled, going from 29 incidents up to 92.
Why don't authorities shoot drones down?
Shooting a drone is considered too risky because of the potential collateral damage from a missed shot.
Most drones use geofencing, which creates a software bubble around restricted areas that block aircraft from entering, but not all drone-makers include the feature and anyone building their own machine can exclude it.
Signal jamming is one of the techniques that have been explored and even training eagles to pick them out of the sky, though Dutch police gave up on its programme as birds were apparently not always doing what they were trained to do and because of the cost.
Can any drone cause problems?
Small, cheap drones for children are unlikely to cause an issue because of the height they can reach, how long their battery lasts and the range they can travel.
The biggest threat comes from industrial drones, which are capable of flying considerably higher and at a further distance from the user. The law states that drones must not fly more than 400ft above the surface and must remain within the user's direct sight at all times.