Concern Over UK Drone Collision Study is Justified

You may or may not have heard about the proposed regulations for drone pilots in the UK. The UK Department for Transport put forward policy proposals that will mean pilots flying drones that weigh more than 250 grams will soon need to register their aircraft and complete a safety awareness test.

Wherever you’re flying in the world, the research at the heart of the proposals could have implications for regulations near you.

Despite all the ‘near-misses’ and fears surrounding drones flying too close to airports, we’ve been waiting to see a study detailing exactly how dangerous a collision between a drone and a passenger jet or helicopter could be. We don’t doubt that these are genuine fears and that the threat is a real one, but the drone community is eager to see appropriate regulations based on evidence, not conjecture.

It would be useful to know exactly how dangerous drones are to larger aircraft, not only from a regulatory perspective but also so that manufacturers can adjust designs if necessary.

So that’s what we were hoping for with the results of this study…

What The Report Says

The Small Remotely Piloted Aircraft Systems (drones) Mid-Air Collision Study was carried out by QinetiQ and Natural Impacts on behalf of The Department for Transport, the Military Aviation Authority and British Airline Pilots’ Association.

The study was conducted using laboratory collision testing and computer modelling.

The first thing to mention is that researchers tested four different types of drone category, separated by weight. These weight categories were an attempt to draw different conclusions for different types of drone. Broadly: consumer, prosumer, professional and fixed-wing hobbyist. In detail these categories were:

• 0.4 kilogram (0.88lb) maximum take-off weight quad, covering the toy market and small hobbyist drones.
•  A 1.2 kilogram (2.64 lb) MTOW quad covering the majority of hobbyist and some smaller professional drones.
• 4 kilogram (8.81 lb) MTOW quad, covering some professional drones and some larger hobbyist drones.
• 3.5 kilogram (7.71 lb) MTOW fixed-wing drone, considered to be representative of professional longer endurance drones and some hobbyist drone types.

The researchers then proceeded to crash drones into aircraft structures at differing speeds to see what the damage would be. This was also partly done with a computer modelling program. These were supposed to reflect scenarios based on real-world situations that were considered to be most likely to occur and to pose the greatest risk. The structures used were:

– Helicopter windscreens (one birdstrike certified and one not).
– Helicopter tail rotors
– Large airliner windscreens

Because there is a huge range of potential speeds at which a drone and a larger aircraft can collide, the research team went ahead and tested a selection of the worst case scenarios. These included the usual cruise speeds of helicopters and the typical speeds of airliners at various stages of low to medium altitude flight.

The Results

A few of the conclusions from the study were:

• Non-birdstrike certified helicopter windscreens could be critically damaged by collisions with a drone in several realistic scenarios. It has also been shown that helicopter tail rotors can also be severely damaged.
• Whilst more resilient than helicopters, the modelling and testing in this study has shown that airliner windscreens could be critically damaged by mid-air collisions with 4-kilogram class quadcopter components, and 3.5-kilogram class fixed-wing drones with exposed metallic components at high, but realistic speeds. These impact speeds would usually be encountered when the aircraft is at higher altitudes, 10,000 feet or above, but aircraft do sometimes operate at these speeds at lower altitudes.
• The construction of a drone can make a significant difference in the impact of a collision. Where the toughest and densest drone components were covered with a plastic casing, or did not hit the windscreen first, the impact of the collisions was lessened.
• Drones can cause significantly more damage than a bird of equivalent mass at the same speed. This seems to be due to the hard metallic components present in drones and means that birdstrike certification cannot necessarily be used as a prediction of complete protection from drones.

Justified Controversy

To say that there’s some controversy around this study would be an understatement. First of all, the DfT has released no further detail other than the summary document – which is 18 brief pages. This pales in comparison to the FAA’s 195-page, peer-reviewed report into small drone safety around people.

Second, the most consequential results of testing came when the researchers assessed collisions with the 4-kg category of drones. However, because the team’s gas cannon was unable to fire a conventional professional drone, such as a DJI Inspire with a camera attached, they were forced to build their own Frankenstein’s monster UAV.

We’d stop short of saying that the device created was intentionally dangerous. But it certainly seems as though this cut corner has led to more dramatic results than there might have been.

As the Drone Manufacturers Alliance Europe (DMAE) spokesman Daniel Brinkweth said in a statement today, “Some of the most alarming findings in DfT’s summary are based on an object that resembles a javelin more than a drone.”

“The study’s authors could not find a way to launch a 4-kilogram drone against an aircraft windscreen, so they mounted two motors, a heavy camera and an oversized battery on nylon arms. This object could never fly, much less encounter an airliner at high altitude. Researchers need access to the full test results to understand whether this is an acceptable shortcut for scientific research.”

The Method of Construction and the Assumption of ‘Cruising Speed’

The choice to devise a custom drone and not use something readily available on the market is all the more strange considering how important minor components and the method of construction was found to be during testing.

Second to that, plenty of the impacts measured in the study – and some of the most dangerous ones – were recorded between drones and aircraft flying at “cruising speed”. However, this kind of speed is usually going to occur well above 10,000 ft – not exactly a drone’s natural habitat.

Speaking to DroneLife, Philip Rowse of ProfiCNC was also critical of the amount of data released by the researchers and the method used.

“If they couldn’t fit the drone in the canon they should have changed methods,” he said. “A sled test with the glass on a frame moving would have been much more accurate.”

The summary raised few concerns about the smallest drones on the market. It was noted that the plastic housings of many drone components served to absorb part of the impact and reduce the severity of a collision. Unfortunately, there was very little detail on this and it doesn’t appear as though the 4kg drone pictured above was put together in a similar way.

“Where is the high-speed video?”

“My biggest concern is that all the actual test data is missing. Where is the high-speed video of the projectile with a measuring backdrop so we can verify the velocity of the impact?”

“When the concern in the public eye is an impact of a consumer drone with an airliner around an airport, the following need to be considered: First, the flight speed of an airliner around an airport. Second, the [fact that the] mass of most consumer drones is sub-2KG. And third, the construction methods of the drones.”

“For example. The Solo drone is made from a polycarbonate material that will deform readily in an impact. Its camera is a GoPro Hero 3+ or 4. The camera weighs 88grams and is retained by a breakaway plastic clip. The motors are surrounded by polycarbonate plastic.”

No Mention of Engines in UK Collision Study?

One glaring omission from the study was the threat that drones could pose to aircraft engines. Restricting the study to collision tests with aircraft cockpits helicopter rotors overlooks what is perhaps the biggest fear of airline pilots: that a drone can be sucked into the engine and cause it to fail.

The fact that this wasn’t mentioned is an oversight, even if it wasn’t tested due to budget restrictions.

Context: The Likelihood of a Collision

In thinking about how serious a threat is, you have to calculate the likelihood of it happening, not just how dangerous it would be in reality. As the study says:

‘It is important to also consider the likelihood of such a collision when assessing the risk. Any existing or
future work on assessing the likelihood of a collision should be considered alongside the findings of this project in order to fully assess the risk.’

The study did indicate that near-misses between drones and larger aircraft are on the rise in the UK. But that rise appears to have plateaued, which isn’t the picture some media reports would suggest. There were 6 in 2014, 29 in 2015, 70 in 2016 and 34 until the end of May 2017.

And it’s also important to mention that those figures are reports of objects ‘believed to be drones’. So they could in all seriousness include several plastic bags or bats.

“There have been no confirmed collisions anywhere in the world between a modern consumer drone and a traditional aircraft, and drone manufacturers are working diligently on technological solutions to prevent any such collision,” Brinkwerth said.

“Many of the shortcomings in this summary report could have been addressed during the research process with more robust participation from all stakeholders. All the major drone manufacturers stand ready to assist with further studies by providing materials for testing as well as research assistance from our experts.”

Why Don’t Manufacturers Carry Out Their Own Studies?

Perhaps the manufacturers will get together and do a study of their own in due course. Although this kind of research doesn’t come cheap, it could – when done properly – go a long way toward easing public safety concerns. Only when that happens will we get regulations that are genuinely proportional to the risks posed by drones.