Hackaday has a good piece that analyzes some of the UK's "drone close to aircraft" incidents and finds them wanting, to say nothing of the media coverage of them. Excerpt:
Hyde, Greater Manchester. The incident location should be somewhere towards the hills in the background. Smabs Sputzer (CC BY 2.0) via Flickr.
Analyzing Incident Reports
So, that out of the way, on to the incident reports. These are proximity reports from the UK Airbrox Board, the body whose task is to apply any of the lessons that can be gleaned from any such incidents to air safety. They are all downloadable in PDF format.
12 o’clock to 1 o’clock on a reciprocal track. Petr Adam Dohnálek [CC0] (Wikimedia)/Andreas 06 [PD] (Wikimedia)
Our first is Airprox Report No. 2015141. A Dornier 328 was above Hyde approaching Manchester Airport on the afternoon of 27th August 2015, at 2800 feet above sea level (about 1500 feet above local ground level) with a speed of 180 knots (207.141 mph). The drone was seen by the pilot, and was a royal blue trirotor, about 50cm in diameter.
As the report notes, this drone would certainly have been breaking the law by flying over the legal 400 feet, and the operator would almost certainly have been using an FPV camera. But let’s return to the report, at 50cm this is not a big machine. If it was a drone, its chances of carrying enough battery power to take it to 2800 feet while also both carrying and powering an FPV camera and transmitter could not be very high at all. Even at ground level these machines don’t have very long flight times, and climbing to that altitude is a power-hungry task. Remember that multirotors have propellers designed for efficiency in the thick air of ground level, and as they climb they have to work ever harder.
There is also the question of it being reported as a trirotor. This is not an unknown multirotor configuration, but such a machine is highly unusual in the UK. Unusual enough for anyone operating one to be noticed, we think.
Moving on, we have Airprox Report No. 2015155, a Boeing 737 departingStansted Airport at 4000 feet and 250 knots (287.696mph) in the late afternoon of the 13th of September 2015. The aircraft reported as a drone had a fuselage 2m in length, the air crew could not say whether it was jet or propeller powered. It was reported as going from the 12 o’clock position to the 1 o’clock position in a reciprocal track.The UK Houses of Parliament. Mike Gimelfarb [Public domain], Wikimedia
Reading this report, we find it difficult to understand how it could responsibly be attributed to a multirotor by any of the media outlets. This describes an aircraft capable of making an extremely tight turn (refer to this page about clock positions in aviation to appreciate this if our diagram isn’t enough) over an airliner traveling at nearly 300mph at 4000 feet (Stansted is a lot closer to sea level than the terrain surrounding Manchester). We’re not fast jet specialists here at Hackaday, but wouldn’t that kind of turn be impressive performance even for a military fighter? Disregarding all the stuff from our discussion of the previous report about the difficulty of a battery powered multirotor achieving that altitude, even in their wildest dreams a multirotor owner can’t make their machine perform like that!
Our credulity now stretched, we move on to Airprox Reprt No. 2015157, an Embraer E170 approachingLondon City Airport at 2000 feet and 160 knots (184.125 mph) around midday on the 13th of September 2015. The aircrew reported “a silver drone with a ‘balloon-like’ centre and 4 small rotors on each corner”, and air traffic control confirmed the pilot had reported the incident while over the Houses of Parliament.Datchet from the air. se71 (CC BY-NC-SA 2.0) via Flickr.
A balloon-like drone would be an unusual machine, but while it may be out of the ordinary it is not an unknown configuration. The Festo machine we have just linked to for example was so unusual as to have received worldwide coverage when it was announced. But like the previous reports the problem we find with this report is the altitude. The power required to get a machine to 2000 feet and stay there without running out of juice and plummeting to earth would push the abilities of multirotor battery technology to the limit. If you notice in the Festo demonstration, it is all performed indoors, without weather or significant altitude.
The real kicker here though is the location. Over the UK Houses of Parliament. If you wanted to run an experiment in how quickly you could get a free ride in a British police car, we’d suggest you try flying an unexpected multirotor in this airspace. It is some of the most tightly-monitored space in the country, full of twitchy security people fueled by The War Against Terror, and one of very few places in the UK where you’ll see police officers carrying guns. Couldn’t it just be that the pilot in fact saw an escaped novelty helium balloon, not entirely impossible over one of the most populated parts of the country?
Gatwick airport from the air. Phillip Capper (CC BY 2.0) viaFlickr
Next on the list is Airprox Report No. 2015162, aBoeing 777 over Datchet climbing out of London Heathrow at 2000 feet and with a speed not reported. We’d expect the aircraft to be under acceleration at this point, so it is likely that it would be moving at a similar speed to the earlier Stansted incident.
The 777 pilot described a quadcopter, about 12 to 18 inches in diameter, and with motors the size of Coke cans on each corner. The encounter was fleeting, only a very few seconds as the 777 was in a steep climb.
There are plenty of off-the-shelf quadcopters that are about 12 to 18 inches in diameter. Container loads of them arrive from China every day, and they would have delighted a million children when unwrapped on Christmas morning. But a couple of things bother us about this report. First there is the weight and power issue we’ve mentioned when discussing the previous reports. A machine that size would not be capable in our view of reaching 2000 feet under control with an FPV camera and staying there for any appreciable time and then returning under its own power. Batteries simply are not available which are light enough to both hold that amount of power and to enable them to do this. Our second concern though comes from those motors. There are large motors for multirotors, it is true. They have higher power output and correspondingly larger electrical power demands, and you might see them on much larger machines driving larger rotors. But would it make sense to fit them to such a small airframe? We just can’t see it. Our friendly expert’s comment on this report was that it sounded as though someone who had seen a picture of a multirotor but had never handled one was trying to describe what they thought one was.
Our next incident is Airprox Report No. 2015172, an Airbus 319 over Poyle on final approach to London Heathrow at 500 feet and 140 knots (161.110 mph) on the morning of the 30th of September 2015. The pilot reported a small drone-like helicopter hovering close to the centre line. He estimated that it passed within 20 to 30 feet of his aircraft.
Unlike the previous reports, this one does not stretch the possibilities of what a multirotor or model helicopter could achieve. A toy drone or helicopter might struggle, but there are enough more capable machines available. It is not at an altitude difficult to reach with a battery-powered aircraft, nor is it beyond the possibility of controlling such an aircraft from the ground. It also finds the Airbus at its point of most vulnerability, when as an aircraft approaching the runway it lacks both the airspeed and airspace to evade another craft or to recover itself in the event of an incident.
There is however one anomaly about this incident which we feel bears further investigation. A multirotor is a small and lightweight machine, and if it were to pass within 20 feet of an airliner at low altitude traveling at 160mph it is likely that it would experience significant turbulence. In simple terms, it would be knocked out of control by the wash of the passing high speed airliner, and there is a significant likelihood that it would not have been able to remain in the air. It is certain that an investigation would have immediately begun to find any wreckage of a crashed drone, yet none was found.
Our final case is Airprox Report No. 2015212, AnAirbus A321 in the final stages of approach to Gatwick Airport in the early afternoon of the 28th of November 2015. The co-pilot reported seeing a stationary drone hovering at about 100 feet over the touchdown zone. The airliner passed underneath it and the co-pilot lost sight of the drone when he was at about 20 feet above ground level.
As with the previous report, this does not push the boundaries of multirotor flight. All but the most ineffectual drones should be capable of hovering at 100 feet above ground level, indeed since it is below the UK 400 foot altitude limit they could do so perfectly legally away from somewhere like Gatwick.
There is however a troubling side to the story that we would like to see an explanation for. Unlike all the other reports, this incident took place within the confines of an active and busy international airport. Airports are crawling with people doing a multitude of jobs, and yet nobody else saw the drone. The incident happened at 13:45 and the police were on the scene at 13:52, an astoundingly quick response for UK police, yet there was no drone. If you take a look at the Gatwick touchdown zone on Google Maps, you will see it is hardly close to the perimeter of the airport, to make a successful escape in that time the drone would have had to fly rather quickly, have an excessive amount of battery power, and somehow be invisible to everyone in the area surrounding the airport. We come back to our theoretical experiment in how quickly a drone pilot could get a free ride in a British police car, we strongly suspect the reality would be that any real drone pilot doing so at Gatwick would find themselves eating porridge in a very short time indeed. If this turns out not to be the case, shouldn’t questions be being raised about the airport’s security?
We Need Better Reports
It is very important to stress that flying a multirotor or any other kind of aircraft in proximity to a commercial airliner is a crime. It’s a particularly dangerous crime, and one which can have disastrous consequences in the event of a collision. We’d go further, and suggest that if anyone is found to have been doing it they should be locked up. Throw away the key, no collecting $200 or passing Go, all the clichés. It’s a crime, and any perpetrators should face all the consequences with maximum prejudice.
We are however concerned by the tone of all the reports listed above, both as they appear in the media and as they are reported in the official incident documentation. It is reported as indisputable fact that they are all multirotors being flown illegally, yet the only evidence presented are somewhat dubious eyewitness reports, either of extremely fleeting views of the craft in question or of craft that very obviously can not be electric hobby multirotors. At no point has anyone produced a real multirotor as evidence, in fact the only incident that featured a collision was found to be with a plastic bag. We feel that reporting these incidents in this way is irresponsible, and not consistent with the high standards we would expect from an aeronautical investigative body.