Were drones really to blame for near-miss with plane?

Call us sceptical, but a recent news story has raised a few eyebrows at Heliguy HQ this week. The article in question? A Virgin Atlantic jet faced a collision at 14,000ft with two drones as it was approaching Heathrow Airport to land.

This press coverage - which has done the rounds on various media sites - got us scratching our heads, deliberating on whether the offending objects were indeed two rogue UAVs (unmanned aerial vehicles), or maybe - just maybe - something else?

Now, this isn't a case of us trying to deflect the issue. Nor is it a desperate attempt to sweep this type of negative drone coverage under the carpet. Let's face it, there's been plenty of UAV scare-mongering in recent months!

I don’t think you could do this with a drone off the shelf. A very custom drone, perhaps, but it would have to be very bespoke, and even then you’d be going some to reach this height

Kevin Morton, Head of Technical at Heliguy

It's also not an attack on the press, or us crying fake news or unnecessary sensationalism in the quest for a juicy story. After all, this headline-grabber has come from an official report published by the UK Airprox Board, whose primary objective is to enhance air safety in the UK.

Indeed, the Board's report states that the Cabin Crew Manager spotted 'two multi-rotor drones' on the right-hand side of the plane, while flying at 320mph over Essex on Valentine's Day. It adds that 'the first drone was slightly low and a bit further out, whereas the second was close in at the same level and seemed to take avoiding action'.

If drones were to blame, they were flying 13,600ft over the legal limit!

The report highlights that the incident occurred at FL140 (to clear this up, FL means Flight Level. One Flight Level is the equivalent of 100ft, so FL140 is 14,000ft) and that based on the evidence provided, one of the drones was 90ft (30 metres) away from the jet (a B787 Dreamliner). The incident was ruled as a Category A risk.

It's hard to argue with an official report. But for us - as drone experts and the leading UAV supplier in the UK - the real talking point has been the height at which these two machines were spotted. According to the findings, the pair of flyers almost collided with the plane at a whopping 14,000ft - which equates to 4,267 metres, or 4.2km. That's high! Very high!

"It is practically impossible for a multi-rotor drone to reach 14,000ft due to the limitations of battery density/ mass. For two drones to reach this height at the same time, in the same location, is extremely unlikely." This is the view of the Flight Safety Board.

To put that into perspective, these alleged drones were flying 13,600ft above the legal limit. A quick check of the law and the Dronecode states that remote-controlled aircraft should fly no higher than 400ft (120m) to reduce the likelihood of a conflict with - ironically enough - manned aircraft.

Make no mistake, a drone flying at 14,000ft is high. Very high. Unusually high!

But that's not to say that the possible culprit(s) in this incident didn't ignore the rules. After all, there are bound to be some irresponsible drone pilots out there who will flout the law, which in turn gives the UAV industry and the vast majority of responsible operators a bad name.

Hopefully, new drone legislation (police to be given additional powers to land, seize and search drones; the extension of the exclusion zone around protected airport boundaries; and a requirement, from the end of November this year, for all owners with drones over 250 grams to register with the CAA and complete an online safety test) will help to stop drone misuse.

'A Drone At 14,000ft? Are You Sure?'

However, the fact that these drones apparently climbed to 14,000ft has sparked a debate in the Heliguy office. How was it possible for two drones to cause disruption at such an extreme altitude?

At this point, it's important to stress that we're not discrediting the Airprox report, rather we are setting out the practicalities, realities and challenges of flying a drone at such a height.

Climbing to 14,000ft - whether at a rapid acceleration or hovering at that height, with factors such as wind speed - would drain the battery of the drone very quickly

So we reached for the specification sheets of the DJI drones that we sell. And let's face it, DJI drones are a good model to go by, considering that the Chinese-based technology giant accounts for the vast majority of the drone market.

A flick through the drones' vital statistics shows that while it could be possible for them to be airborne at this height, it does seem highly unlikely and it would take some going to almost collide with a jumbo jet at 14,000ft.

Take the Inspire 2 for example, which is one of the fastest drones in the DJI ecosystem. Its maximum ascent speed is 19.7ft/s. So, it would take the drone almost 12 minutes to reach 14,000ft. And that's at full throttle; a manoeuvre which would drain the battery very, very quickly. Then it would have to allow time to descend - either 13.1ft/s vertical fall or up to 29.5ft/s on the tilt.

A DJI Inspire 2.

The Inspire 2's maximum battery life is shy of 30 minutes - but this is hovering at sea level with no wind. Imagine how fast the power would drop if the operator went for a rapid all-out climb. Or, if the drones were simply hovering at 14,000ft, factors such as wind speed would have a major say in the staying power of that drone.

A look at other DJI drones, and the Phantom 4 and the Mavic 2 have very similar ascent speeds and flight times to the Inspire 2.

"It is highly unlikely that any drones were involved in this reported Airprox," - the Flight Safety Board

There are also drones in the enterprise-specific M200 Series, which have a battery life of up to 38 minutes, but a slower ascent speed. And even with this longer endurance, it would still be going some to reach such heights. The Matrice drones also have a maximum service ceiling above sea level (the maximum altitude where a 100 foot per minute climb can be maintained) of 9,842ft (3,000metres).

A DJI M200 Series V2 drone.

On the issue of wind speed, these DJI drones range in maximum wind resistance, from 10 to 12 m/s - or 23mph to 27mph. Admittedly it's a different day, but, to put this into context, the wind speed at 4,200metres at Brentwood (where the incident happened) yesterday was 46mph, according to windy.com.

At 14,000ft, you are at the fringes of what you can achieve when it comes to radio transmission, says Heliguy's technical expert

As our Head of Technical, Kevin Morton, says: "When a drone has a 30 minute flight time, that's at hover. When the drone is in a climb at full throttle, that time is reduced. And that's not including air-resistance changes and wind speed which would also affect battery life. You've also got the issue of radio transmission, from the pilot to the drone, and at 14,000ft, you would be on the fringes of what you can achieve."

There are others, too, in the industry who have questioned the incident in February. Reacting to this week's news report, Matt Bailey, from DJI, took to LinkedIn to cast his doubt, writing: 'Is it just me or doesn't something quite add up here. 14,000ft? Are you sure?'. His post prompted an array of likes and similarly sceptical comments.

If not DJI, then perhaps another drone? But Kevin still has his doubts.

He said: "I don't think you could do this with a drone off the shelf. A very custom drone, perhaps, but it would have to be very bespoke, and even then you'd be going some to reach this height."

Two Multi-Rotor Drones at 14,000ft - 'Practically Impossible'

The Flight Safety Board (FSB) has also rubbished the claim that two drones were involved in the incident, branding the alleged sightings as 'preposterous'.

The FSB is a group of experts who analyse Airprox data using a Reality Check System to evaluate the likelihood of an event having actually involved a multi-rotor drone. In their opinion, any score below 0 is considered unlikely to have involved a multi-rotor drone. This is based on numerous criteria, such as altitude, wind speeds, the weather and where the report has come from.

The Flight Safety Board says: "The B787 was flying at 227 knots. If a drone was 30m away from a cabin window it would flash past in a few milliseconds - it would be impossible to identify."

Needless to say, this particular incident has made it onto their radar and having been pushed through the Reality Check System, it scored an unconvincing -75. Ouch! Their findings are shown in this table below:

Refuting claims that two UAVs were involved, the FSB states: "It is practically impossible for a multi-rotor drone to reach 14,000ft due to the limitations of battery density/mass. For two drones to reach this height at the same time, in the same location, is extremely unlikely. The B787 was flying at 227 knots - if a drone was 30m away from a cabin window it would flash past in a few milliseconds - it would be impossible to identify."

Going further to dismiss the accusation, the FSB says: "Commercial off-the-shelf multi-rotor drones are not capable of reaching 14,000 feet.

"Considering the maximum altitude that a drone could physically reach (approximately 6,500ft for a DJI Phantom 4, firmware limits notwithstanding), the drone would have to immediately descend as soon as it reached that altitude.

"The chances of an airliner flying past at exactly the moment that a drone reached its maximum height seem to be very small. The chances of this happening with two drones, 30m apart, seems an order of magnitude smaller.

"It is significant that the flight crew did not see these ‘objects’. The reported objects, at the reported distances, should have been clearly visible to the flight crew from their far superior vantage point, as they were approached.

"It is possible that the flight crew correctly dismissed the objects as distant manned aircraft without thinking about it.

"The chances of an airliner flying past at exactly the moment that a drone reached its maximum height seem to be very small." That's the view of the Flight Safety Board

"The Board concluded that it was highly unlikely that any drones were involved in this reported Airprox."

The FSB believes that claims like this have led to 'unnecessary and overzealous government regulation which will do irreparable harm to the drone, model aircraft and, in the longer term, aviation communities and industries'.

Some Drone Reports Have Been Wrong

Also, the Airprox report is taken from an eyewitness account - the Cabin Crew Manager, and not the pilot, who spotted a drone which was 90-feet away while the plane was travelling in excess of 300mph. Just throwing it into the mix, but could it have looked like a drone, but indeed been something else?

Not only this, but the report says that the incident occurred at 4.55pm. According to timeanddate.com, the sunset in London on February 14, 2019, was 5.13pm - less than 20 minutes after the sighting. With this in mind, with the light fading rapidly and darkness setting in, how good would visibility have been at this time? Could a drone really be picked up in the impending gloom, especially as the report makes no mention of the drones having lights.

As we have seen with previous cases, people have had a tendency to point to drones as culprits. But there have been many stories where reports of UAVs wreaking havoc have ended up being wrong, with the actual villains turning out to be a plastic bag (UK, 2016), a bat (Australia, 2017) and a balloon (New Zealand, 2018).

Some reports of drones have turned out to be wrong, with the objects, in fact, being a plastic bag or a balloon

Then there was the incident at Newark Airport in January. Officials with the Federal Aviation Administration (FAA) said that they received two reports of possible drones operating nearby, one from a Southwest Airlines pilot and the other from a United Airlines pilot who spotted what they believed was a drone in the air as they prepared to land. But later, an FAA spokesman said that the agency had been unable to independently confirm the sightings.

At the time, industry experts pushed back against the reports, claiming that the objects could have been balloons, plastic bags or space junk. Adam Lisberg, spokesman for DJI, questioned the drone sightings in a tweet, asking how pilots in a plane travelling 250mph could see something the size of a dinner plate at 3,500ft. He added: 'Whatever they saw, it probably wasn’t a drone.'

Drone Detection Helps To Combat A Threat

It all makes for an interesting debate. Perhaps drones were to blame for this near-miss in the Essex skies earlier this year. It's not completely impossible and if they were the culprits, then let's hope there is no repeat! But maybe, just maybe, all is not what it seems, and taking certain factors into account, there could be another reasonable explanation?

Despite all of this, it is still fair to say that, in some quarters, there is apprehension about drones - perhaps fuelled by the Christmas-time disruption at Gatwick. To help mitigate and deter rogue UAV pilots, Heliguy specialises in drone detection, helping the likes of airports, prisons and stadia arm themselves with suitable technology to combat a potential threat. After all, the incident at Gatwick showed just how costly a drone attack can be.