How dangerous are drones to aircraft?

Any midair collision with an object is dangerous to aircraft, as exemplified by the crash of US Airways Flight 1549 in January 2009. Capt Chesley Sullenberger steered a passenger jet carrying 155 people into the Hudson River after it hit a flock of Canada geese shortly after taking off from La Guardia airport in New York City. The birds destroyed both aircraft engines.

The weight of a Canada goose – between 2kg and 6.5kg – is exceeded by some professional-quality camera drones. Pilots have called for more testing on the potential impact of a drone on an engine – tests that manufacturers routinely apply for bird strikes – but this would be expensive.

Gatwick airport disruption: police still trying to catch drones after flights cancelled – live Read more

How common are near misses between drones and aircraft?

The rate in the UK has tripled since 2015. The UK Airprox Board (UKAB), which monitors all near misses involving commercial aircraft, said there were 92 between aircraft and drones in 2017. That was more than three times the number in 2015: 29. In 2016, there were 71 and the data is clearly tracking the growth in drone use.

What are the UK regulations?

It is against the law to fly a drone higher than 120 metres or in restricted airspace such as near an airport. Further restrictions apply if the drone is fitted with a camera. The Dronesafe website, operated by the aviation watchdog and national air traffic control, outlines a series of guidelines for drone flying, including keeping the drone in eyesight at all times.

What can be done to stop them flying over airports?

Prisons could help provide the answer. The government is looking at introducing an anti-drone system to stop drug smuggling in English prisons following a successful six-month experiment in Guernsey. The SkyFence system blocks radio signals around a prison whenever drones are detected and is used to prevent them from dropping drugs to inmates.

But jamming the signals used to control the drone could be risky in an airport, where the risk of inadvertently damaging other critical communications may be too high.

Endangering people by flying a drone illegally can lead to a custodial sentence of up to five years, but police have found it very difficult to identify the operators of drones that have been spotted by pilots, hence the calls for a mandatory register of drones and their users, and for “geo-fencing”.

How easy is it to break geo-fencing restrictions to fly a drone?

Very easy. Some drone manufacturers, such as China’s DJI, operate GPS-powered “restricted zones”, which will prevent operators from flying over areas such as airports, prisons and sporting venues. But even those restrictions can be unlocked for users who contact the company with appropriate authorisation – and companies such as Russia’s Coptersafe will perform the unlock for anyone who can afford to pay.

Other drone manufacturers do not implement those restrictions, as the patchwork of local, national and international laws leave companies uncertain as to their own obligations, and with some models of drone lacking the GPS control required to perform any sort of gating.

How else can a rogue drone be tackled?

Authorities around the world have explored a variety of methods. One of the simplest involves throwing a net at the offending vehicle, either by firing it from a cannon on the ground, or dropping it from a second drone. The rotors of a quadcopter rapidly get tangled in the netting and the device plummets to the ground.

At the other end of the spectrum, Dutch police have explored using specially trained eagles to attack drones.

How long can drones stay airborne?

A typical consumer drone, powered by a rechargeable battery, will have a flight time of about half an hour. Since more batteries add more weight to the vehicle, it is hard for manufacturers to achieve much improvement on that limit, with 30 minutes being the flight time of everything from a £60 Parrot Mambo to a £1,589 Phantom 4 Pro.

That means multiple hours of continuous operation takes more than one drone and a significant amount of preparation. Swapping in spare battery packs can get a drone back in the air quickly, but those packs then take a long time to recharge.

How far can they fly?

Even with a 30-minute flight time, the range of most drones is limited by connectivity requirements, rather than fuel. Basic consumer drones will connect with their controllers over bluetooth or wifi, giving them a range of a few hundred metres at most, but more expensive “prosumer” devices use purpose-built radios to communicate over longer ranges of up to five miles.

With enough money, however, there is effectively no upper limit: companies such as Botlink and Globe UAV sell add-ons for professional drone operators that allow them to control their craft over 4G, meaning they can fly anywhere with cellular reception.

Could the Gatwick drone incident be an organised protest?

There will be plenty of speculation about who is behind the Gatwick drones, given the impact they have had, but the fact that the disruption was sustained for a long period points to a deliberate act. Sussex police said it was “a deliberate act to disrupt the airport”, but added: “There are absolutely no indications to suggest this is terror related.”

Why not just shoot down the drone?

Drones aren’t (usually) bulletproof, and a well-placed shot will end their journey sharpish. But, for obvious reasons, police are loth to discharge weapons in sensitive areas like airports: bullets are dangerous on the way down, as well as the way up, and the risk of collateral damage from a missed shot is high. And the chances of a shot being missed may be quite high. A small drone moving rapidly almost half a kilometre in the air presents a difficult task for anyone but a trained marksman.

Despite that, police carrying long-range rifles have reportedly been placed along the runway, ready to shoot down any trespassing drone.

How could the operator be tracked?

A long-distance drone typically communicates with its operator using a high-powered radio connection. That can be traced with a directional antenna, eventually leading back to the operator themselves – but only while it is in operation. Unfortunately, the police have found, the operator appears to be aware of that fact: “Each time we believe we get close to the operator, the drone disappears,” said Supt Justin Burtenshaw, the airport’s policing commander. “When we look to reopen the airfield, the drone reappears.”

• The graphic in this article was amended on 21 December 2018 because an earlier version said drones must not fly within 50 metres of crowds and built up areas. This has been corrected to say 150 metres.



