In this AAIB accident investigation, published in 2021, a rather terrifying event is described in which a 3m long, 95 kg remote-control nearly-home-built drone is flown at speeds of up to 25 m/s below 100 ft by a crowd of spectators before becoming stuck in a climb at around 2000 ft/min. Its operators could not stop it -- its "kill switch" failed to operate -- and it rose up to the bottom of class A airspace at 8000 ft before the battery ran out. The drone later crashed in a field, with no fire, and no injury. It was intended as a large-scale demonstrator prior to a manned aircraft.

It was found that this occurred because of radio interference, the fact that the operators reduced the transmitter power of their radio control system due to CAA regulations, and arguably that the drone "was not designed, built or tested to any recognisable engineering or airworthiness standards". They received a paperwork-driven authorisation to fly with no physical inspection of the device -- and the photos show a lot of arduinos and loose wires held together with cable ties. Most of the report's 15 recommendations are aimed at the CAA to prevent an event like that ever occurring again -- clearly a 95 kg device crashing at around 5000 ft/min with flammable lithium batteries is very dangerous.

I find it odd that nothing else was done about this at the time. Within minutes of becoming uncontrollable, the drone was straight in the middle of the flight path near Gatwick and posed a danger to both aircraft and, if it crashed in the wrong place, people below.

My questions are therefore:

  1. What actions would a country or otherwise competent authority (like the CAA) take in this eventuality, and prevent the aircraft from posing a risk to passenger aircraft?

I realise that it is clearly better to avoid it happening in the first place! Short of shooting it out of the sky (which presumably is an absolute last-case option) it seems a very sticky situation to be in -- no transponder, no functioning radio, and risks above and below.

  1. Is there a standardised response in this sort of situation, if e.g. aircraft on the final approach to gatwick get a radio message essentially saying "be on the lookout for a 95 kg, 3 m long, untracked drone flying vertically upwards at 2000 ft/min somewhere nearby"?

Would ATC try to invite flights to use an alternative approach path -- e.g. even one that involved landing with a tailwind, to avoid the affected area?

If it helps, here are some pictures of the drone in question, all taken from the AAIB report:

The drone in question Drone in an uncontrollable climb Crashed drone Broken drone kill-switch

(And a Youtube summary published by the AAIB)

  • 1
    $\begingroup$ I've tried again to reword this to make it less opinion based. If anyone else wants to have a go, feel free -- I hope that the question is of interest at any rate. My PPL training has unsurprisingly not covered "an unknown, uncontrollable aircraft may hit you from below" -- rather just that I should give way to uncontrollable aircraft (like balloons) if I encounter them. $\endgroup$
    – Landak
    Jan 23, 2022 at 12:39
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    $\begingroup$ Just don't forget that the sky is full of lots of things besides runway drones-- like birds-- $\endgroup$ Jan 23, 2022 at 13:52

1 Answer 1


The scariest thing for many government bureaucrats is any new area of enterprise. Those things tend to evolve quickly, and often in unexpected directions, requiring adaptation which is difficult when you like things just the way they are.

To keep things simple, I'd answer your two questions with:

  1. Regulators can easily prevent these kinds of events by enacting expansive and expensive regulations that effectively kill all further activity in the field. The downside is that it's like killing your horse to keep it from escaping the stables.

  2. I fly often near an area where the government tests various types of UAVs. The ATC mentions their presence at times, just like for any other traffic. Sometimes they show up on the don't-hit-me idiot box, too.

If you want my 5c, I'd say that once a UAV gets large enough it needs a transponder so others will see it easier in their Nintendos. But it's not just about size, because even a large object is pretty much harmless if it has low density.

Whatever the optimum formula may be, I expect regulators to get it wrong if they try to define it too early. The worst thing would be for them to use early outlier events to define policy that kills a promising area of air mobility.


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