back to article Sheer luck helped prevent mid-air drone glider prang in Blighty

A drone being flown next to an active airfield on New Year’s Day caused a serious risk of an in-flight collision with a glider trying to land, the UK Airprox Board has ruled. The drone, flying above Dunstable, a market town 50km north of London, came within 4.5m (15 feet) of the glider as it was completing its circuit and …

  1. Anonymous Coward
    Anonymous Coward

    surely the drone would have been knocked out of the way by the glider?

    1. DavCrav

      "surely the drone would have been knocked out of the way by the glider?"

      Sure, but in a kind of crashy way, that might not have gone so well.

    2. Anonymous Coward
      Anonymous Coward

      "surely the drone would have been knocked out of the way by the glider"

      Well, yes, *after* causing damage to the glider, which, like many other types of small aircraft, isn't bird strike certified or designed to withstand an impact with a drone.

    3. Anonymous Coward
      Anonymous Coward

      It depends on the speed of the glider (squared), the mass of the drone, and the position of the impact.

      There was such an accident last year in the Netherlands:

      The drone operator, typically, ran away. Luckily the damage was relatively small, but structural repair was still needed. The accident happened in airspace closed to drone operations.

      The composite wing of a glider consist of an upper and a lower shell. These are glued together at the leading edge, the wing spar and the end spar. Composite glue joints do not like impact loads, so a sufficiently high energy impact (heavy drone, glider flying close to Vne) at the leading edge of the wing could in theory compromise the forward torsion box, which then could potentially result in aeroelastic effects (flutter) destroying the wing.

      At that point, one has to hope that the chute will deploy in time.

      1. Mark 85

        At that point, one has to hope that the chute will deploy in time.

        On final? Doesn't seem likely that it would given altitude and then there's how fast the pilot can react.

        1. Anonymous Coward
          Anonymous Coward

          "On final? Doesn't seem likely that it would given altitude and then there's how fast the pilot can react."

          The discussion is on gliders impacting with drones. There is no natural law saying that the impact has to take place on final (the dutch glider was not on final). The glider would also not fly at Vne on final. Generally speaking, one needs at least 800 m of altitude in order to sucessfully jump from a glider. Anything below gets iffy. Therefore, it might prove difficult to survive a catastrophic structural failure on final unscathed.

      2. Mayday

        Chute etc

        "At that point, one has to hope that the chute will deploy in time."

        I'm a skydiver and a pilot.

        Finals (unless a straight in approach) are normally at around 500ft. A parachute typically used as a pilot emergency rig would not be open in time at that sort of height, particularly if the glider canopy needed to be jettisoned and the harness released, bearing in mind during this time a damaged wing will be generating less/no lift and the glider will also be unstable and losing height.

        1. Ptol

          Re: Chute etc

          Paraglider reserve parachutes are different from parachutes worn by skydivers. Principle difference is that they are shaped like an old WW2 parachute with the middle pulled down, making them donnut shaped. A freshly repacked reserve can open in around 150 ft, but are typically quoted as 500ft by the manufacturer.

          As the glider was on finals, taking evasive action also has other consequences - like do they still have enough energy left to safely reach the landing field?

          1. Orv Silver badge

            Re: Chute etc

            Frankly, on final you're concentrating on your touchdown point; a drone collision is likely to take you by surprise before you can do much. It's not so much about energy as it is about time to react. In particular, you can't turn a glider suddenly; their large wingspans give them very slow roll rates.

            The geometry really doesn't help you here, either. A drone on a collision course won't be moving in your visual field. It'll be stationary except for growing larger. And may very well be against a cluttered background of trees.

            Other than the startle factor, though, in the pattern is probably one of the better places to hit a drone; you're moving relatively slowly, and you're close enough to the field that damage to the nose or canopy that lowers your glide ratio probably won't force you to land short.

            The worst time, IMHO, would be during a typical competition finish, with gliders coming in low, heavy, and close to Vne. Maximum impact potential, and minimal time to regain control.

      3. Orv Silver badge

        That's the high tech version. The gliders I flew had wooden wings with painted fabric coverings. The fuselages were steel tube space frames, also fabric covered. This is a time-honored construction method that's reasonably light and very easy to repair, and can handle some pretty heavy aerodynamic forces. But it's not tolerant of point loads. It's entirely possible to put your thumb through the fabric if you apply force in the wrong places.

        A typical example of this kind of wing construction, with the covering removed:

        The canopies in these gliders were blown plastic, maybe 1/8" thick. I saw one cracked after a pilot hit his head on it during a sharp maneuver.

        Aircraft like this, while a bit crude, are very, very common still. They're actually fairly safe -- in a landing accident, most of the energy tends to be dissipated as the wooden wing structure crumples. But bird strikes have been known to cause serious damage to both plane and pilot, and I think the risk is definitely there with drones.

    4. MrZoolook

      Surely the brick would be bounced out of the way of the window...

  2. Adrian 4

    I think it would have had to hit the canopy or get wedged into a control surface to cause any trouble, Gliders aren't noted for having problems with engine ingestion.

    Not that I'm downplaying the incident. Model flying is regulated for safety. I have no idea why drones aren't operated in exactly the same way, which would keep them away from the edge of an airfield. I also think Dunstable Downs is a dreadful place to fly a drone - it has strong, gusty winds. Kites are far more suitable.

    1. AndrueC Silver badge

      Gliding can be dangerous.

      Being hit by falling bodies is less good. That actually happened at an airfield very near where I live.

      Mind you it was also Hinton where Mr. Farage got into a spot of bother when his political aspirations got the better of him.

      1. TheDillinquent

        Re: Gliding can be dangerous.

        Shame the c**t wasn't killed.

        Farage I mean.

    2. Anonymous Coward
      Anonymous Coward

      "I think it would have had to hit the canopy or get wedged into a control surface to cause any trouble"

      Well, I'm not convinced about the impact strength of a typical glider wing leading edge. It's not as if they're designed to fly in adverse weather.

      1. Jason Bloomberg Silver badge

        I imagine the "WTF?" moment could compromise the landing of a less experienced pilot or one who had not been previously aware of the drone.

        I guess it's not quite so extreme as the emergency stop one may automatically do in a car when something jumps out unexpectedly, but it's going to cause some reaction and be distracting at least.

        1. I ain't Spartacus Gold badge

          I guess it's not quite so extreme as the emergency stop one may automatically do in a car

          What are you talking about? I've seen footage of planes doing emergency stops. Such as this documentary footage of an aerial pigeon hunt (video with sound - safe for work).

      2. Adam 52 Silver badge

        "It's not as if they're designed to fly in adverse weather."

        They're designed to flying inside a CuNim, that's adverse enough. And this was a K21, so built bombproof (well, ignoring Dunstable's last high profile K21 incident).

      3. Denarius Silver badge

        adverse weather ???

        what power pilots call turbulence, we call lift. Glass and carbon fiber gliders are remarkably strong for their weight. Even the Libelle in illustration would cope with wing strike probably. On tailplane entirely different story. Cruciform are stronger but lower performance slightly. The modern T tails are vulnerable. As for bailing out, rule of thumb is below 4000 feet there is little hope. I know of one recent case where pilot _left_ damaged glider at 1000 approx and hurt ankle on landing as chute had just fully opened. He had started to exit around 4000 feet.

        My club had a similar drone prox incident recently. Car numbers will be reported to police.

        1. Orv Silver badge

          Re: adverse weather ???

          I think the trick here is aerodynamic loads and impact loads are very different.

          I've seen wings that were designed for +4g/-2g loads get damaged on the ground by even mildly rough handling.

          1. Eddy Ito

            Re: adverse weather ???

            Which is the exact point. It's potentially subjecting the structure for loads that it wasn't originally designed for. There is no telling the impact angle of a drone that moves in all three dimensions with relation to a flying plane especially a glider that is flying slowly, quite near stall speed, as it comes in for landing.

            Sure, it might take a pigeon on the leading edge of the wing but if it comes from an odd angle and tears up the control surfaces it's a whole different story.

      4. Ian Johnston Silver badge

        Well, I'm not convinced about the impact strength of a typical glider wing leading edge. It's not as if they're designed to fly in adverse weather.

        On the contrary, gliders are designed to fly in the shittiest weather imaginable, and are extremely strong. I owned a plywood one which was good for +6G/-4G, with maximum design loads of +9G/-7G. Wing leading edges in particular are made very robust.

    3. Anonymous Coward
      Anonymous Coward


      ...the biggest risk here was that it distracted the pilot at a critical time in the flight*. Whether or not it could have damaged the glider is almost irrelevant.

      * for me that's the terrifying period between getting on a plane and the cabin crew serving the first gin.

      1. Sgt_Oddball

        Re: Surely...

        To the pilot?

    4. Eddy Ito

      Engine ingestion, provided it isn't a motor glider, no but gliders or sailplanes are rather lightly built and it would be possible to produce very extensive damage that even if landed safely would be very expensive to repair and far in excess of the value of the drone and quite possibly the drone's owner. Also keeping in mind that some sailplanes attain 250+ kph an impact with a drone to the canopy could easily prove fatal as the canopy won't stop much as proved by an eagle a few years back.

  3. Andy 73 Silver badge


    Understood that this should be given respect, as a collision is potentially fatal.

    However, to link this with tightening drone rules is disingenuous, as the existing rules were clearly already being broken by the drone operator. Most consumer drones will not support flight above 121 meters without confirmed user intervention, so the operator appears to have been knowingly and deliberately flouting the existing rules.

    Unfortunately, some commentators will abuse this incident in order to push an enforcement agenda that does not solve the issues at hand.

    1. I ain't Spartacus Gold badge

      Re: Hmmm...

      Linking this incident with tightening drone rules may be unfair. But if there's an increasing number of these kind of incidents, then rules will get tightened. The nice thing is that at least we'll have some evidence to go on, as aviation is tightly regulated and makes quite a lot of effort to investigate incidents that don't actually lead to accidents.

      If we get a rising number of incidents, despite the existing rules, then it's likely that those rules will be changed. All that may achieve is to ruin sensible peoples' fun while leaving the idiots unaffected, but nobody said legislation had to be good. Just that it had to be passed.

      1. Andy 73 Silver badge

        Re: Hmmm...

        The problem is that the more 'extreme' you make the rules, the more you tempt people to just ignore them.

        Passing bad legislation because you 'have' to can have quite unfortunate side effects.

      2. Paul 129

        Re: Hmmm...

        Endangering a flight. Locally its a 20 year sentence. Absolute liability, so you can't cry I didn't mean to.

        I'd expect it to be the similar in other jurisdictions, especially given various international agreements.

        Murderers can get less. So get the police to really investigate, charge and jail the people involved.

        Theres a good chance that the person has a mobile phone, so there's only so many people in the cell zone.

  4. Anonymous Coward

    Sheerluck Holmes, the great detective prevents another tragedy.

  5. Neil Barnes Silver badge

    Dunstable ridge is my local paragliding site

    At the time of the incident, from the description in the airprox report, the glider was about to turn for his final approach to the landing field; heading *towards* the ridge and about two hundred feet above the landing field; he would have been at the approximate height of the top of the ridge.

    Whether an impact caused damage or not I think i can say with some authority that it occurring at a critical phase of the flight is certainly not something I would want as a pilot; you only get one go at landing a glider.

    In most of the country's paragliding sites, it's a question of just turning up and going (with necessary permissions from the site owner/local club). To fly my paraglider at Dunstable, I am required to complete not only a site briefing, but be of a certain experience (or be flying with a coach) and have passed a written exam about the rather complicated airspace. Depending on my ambitions for the day, I may also have to register myself as being in the airspace.

    We keep good separation from the kite-flying areas and we have defined exclusion zones to allow the sailplanes to make their final turn and landing approach. The thought of someone up on the ridge flying a drone while I'm in the air terrifies me.

  6. 0laf Silver badge

    I guess most glider pilots would be pretty pissed to have their rather expensive toys* damaged by some plonker flying his toy where it shouldn't be.

    *I say 'toy' because there isn't a lot of commercial use for gliders but I've been gliding quite a few times as a kit and loved it. I'd thoroughly recommend taking an experience flight to anyway.

    1. Thicko

      Your careless use of the word 'damage' glosses over the serious risk to life not just property. Most non pilots dont seem to get how badly things can go wrong with even apparently trivial damage to an aircraft.

  7. GlenP Silver badge

    The existing rules are clearly being flouted all the time* but short of significant penalties I'm not convinced tightening them will make much difference.

    *Like the drone being flown at a car event last weekend, well within 50 metres of a pub building, a gathering of people in the car park and within a few metres of a major road junction which was probably the worst of the three.

  8. TheRealRoland

    Guess i'm too late to preempt the commentards saying 'but it doesn't have an engine, so how could it damage the glider?' It would just 'slide off' or 'bump it out of the way'.


    Put blinkenlights on them, dayglo orange mandatory colors. And. Don't. Fly. Near. An. Airport.

    Follow. The. Frikkin. Rules.

    1. Neil Barnes Silver badge


      This was not only in the immediate vicinity of the LGC aerodrome, it was in the class-D controlled airspace of Luton Airport.

    2. BlinkenLights

      Sorry, I don't do dayglo.

    3. Orv Silver badge

      I think most people saying "how could it do damage?" would still be uncomfortable if a similarly sized object were chucked off an overpass at their car.

  9. The Bionic Man

    It's also illegal to fly a drone within 5 miles of an airport.

    1. Mark 85

      Just because it's illegal doesn't stop idiocy. We all understand that the rules are there for a damned good reason. Idiots seem to not have this mindset.

  10. Dodgy Geezer Silver badge

    It would have been...

    ...VERY unlikely to have caused any serious damage to the glider. But VERY likely to have distracted the pilot at a critical time in the flight.

    And the drone sounds as if it was flying illegally under current rules. So producing a new law is unlikely to have much of an effect on that drone flyer.....

    1. druck Silver badge

      Re: It would have been...

      The risks are not just from a collision or distraction, but also from attempting to avoid the drone. When an aircraft is turning finals, it's airspeed and altitude are low, attempting any sudden maneuver risks a stall with very little possibility of a recovery.

      1. Denarius Silver badge

        Re: It would have been...

        low and slow ? not unless pilot is ignoring their training. One of the landing checks is ensure safe speed near ground which is 1.5 x stall speed plus 0.5 wind speed. 65 knots in my area, but has been over 70.

      2. Ian Johnston Silver badge

        Re: It would have been...

        When an aircraft is turning finals, it's airspeed and altitude are low, attempting any sudden maneuver risks a stall with very little possibility of a recovery.

        Altitude may be low-ish - typically 350' AGL - but speed bloody well shouldn't be. You stick on extra speed during the downwind leg of the circuit for precisely this sort of situation.

    2. imanidiot Silver badge

      Re: It would have been...

      See the link posted earlier to the photos of a glider that hit a drone in the Netherlands:

      A hit with a mid size consumer drone was enough to split and delaminate the winglet on a modern glider (and thats one of the stronger and less vulnerable parts of the wing on a modern carbon fiber composite aircraft). A hit on an older wooden wing is going to be much more damaging. The torsion box formed by the leading edge is only about 3 to 4mm thick plywood. The nose of the fuselage no more than 2 usually. Imagine wat a Phantom quad is going to do when slammed into something like that at 80 km/h+.

  11. RossGoodman

    I thought this was a "drone glider" crash rather than a "drone vrs glider" crash.

    Was interested to read about the tech in drone gliders ....

  12. Anonymous Coward
    Anonymous Coward

    Drones are a new thing, worryingly obtainable and flyable by unskilled people. This is different to normal model aircraft; typically you'd go to a club / organisation where normal model aircraft flying etiquette is entrenched as part of the learning to fly process.

    The regulatory approach for drones is, unfortunately, going to have to evolve to deal with the worst types of owner / operator (likely to be an outright ban ultimately, or at least heavily licensed). This is going to spoil it for the more considerate sort of owner / operator, the sort who does actually think before they do something.

    Regulation works as follows; you keep upping the penalties until you get the behaviour you want. With traditional model aircraft the regulations are light weight and sensible, backed up by a fairly strong club tradition that ensures that the vast majority behave nicely. It will be different with drones.

    The regulations we have now are clearly beginning to not work as drone ownership proliferates. This will result in heavier fines (won't work; anyone stupid enough to fly a drone next to an airport is unlikely to bother to read up what the penalty for doing so is. And the police aren't really able to catch people doing it anyway). That will escalate to jail time (won't work - same reason). That will lead to control of sales (will work to some extent).

    The only sure way is to make it so that you go to jail if you fail to shop your mate who has a drone and misuses it. That is, your mate posts drone-originated video from near an airport, you get on the phone to the police. Or something like that. You fail to tell the police, and the police can show that you know who they are and what they were doing, you either risk jail or you drop them in it. Easy choice in my mind.

    Of course, that is incredibly draconian, but how else are we supposed to stop total idiots cocking about near airports?


    Incidentally, this kind of legal compulsion already exists. If you know someone is plotting a terrorist offence, and you fail to tell the police, you can go to jail. People have been convicted and imprisoned for this very thing. And if you squint only a little bit, unthinkingly flying a drone near, say, a landing airliner is risking causing the same degree of death and carnage as premeditated terrorist attack on the same airliner. So perhaps such a dib-them-or-else penalty is not so draconian as it might first appear...

  13. Claptrap314 Silver badge

    Kites to only 120m at an optimal place? Wow. I grew up in western Kansas. I've seen kites out with more than a mile of "string". I'm pretty sure that I've personally come near or broken that limit.

    1. Anonymous Coward


      Yes, you can end up in Oz, if you're not careful...

      (looking for the silver shoes to get back)

      1. CJPM

        Re: Kansas...

        Yes, you can end up in Oz, if you're not careful...

        (looking for the silver shoes to get back)

        You will not get back that way, look for the ruby slippers instead.

    2. Martin Gregorie

      Kites to only 120m at an optimal place?

      Rather necessary. If you're at or above 153m you're infringing controlled airspace and likely to be in deep dodo if you or your toys are spotted there. Luton have decent radar.

      I've flown at Dunstable and, consequently, know that London Gliding Club standing rules are that you do not go past the top of the ridge, which forms the southeast edge of the airfield and is where the kite fliers were standing, because the Luton Class D CTR (controlled airspace) is not far beyond it and extends from the surface to 5000ft. The CTR is a no-fly zone unless you're under ATC control. Northwest of the ridge the Class D airspace forms a shelf, with a lower limit of 500ft, that extends most of the way to Leighton Buzzard.

  14. andy gibson

    time to....

    start arming all aircraft? :-)

  15. Nursing A Semi


    In the name on fair, balanced and unbiased reporting I assume you interviewed the drone pilot to ascertain the luck element rather than the skill shown avoiding a collision with the glider?

    1. Chairman of the Bored

      Re: Soooooo.

      @nursing a semi,

      Nice! But didn't get a rise out of the pilot I ran it by. Former fighter pilot. Said "the only luck here is with guys who cannot fly. You're lucky there are guys with balls and skills like me overhead.". Oi!

      Q: how do you know if there is a fighter pilot in the room?

      A: don't worry about it, I'm sure he will tell everyone quickly

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