What Happens When a Drone Hits a Plane?

There's still a mysterious black drone in Brooklyn, and the FBI can't find it. Last week it appeared just 200 feet away from a passenger jet—that's too close. What if it'd hit it? Bad things. Bad, dangerous things.

Planes are big, heavy, and mighty looking. But they're essentially fragile machines that require a lot of things constantly going right in order to stay in the air—if even a small drone were to make contact, that makes a tough equation even more fraught. But rather than just looking at the sky and yelling "Oh Christ!", we talked to some people who know jets.

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Gizmodo pal David Cenciotti is a private pilot and former member of the Italian Air Force. So, David, what happens when a (small!) drone hits a big plane? "Anything hitting a plane configured for landing, hence slow and close to the ground, can theoretically cause a disaster." That sounds bad. What kind of theoretical disasters are we talking here? David says there are many, many ways for the drone to hit the fan:

  • FOD (Foreign Object Damage) in one of the engines: the Boeing 777 is a two-engine liner. Let's imagine the drone was sucked by one of the two engines. The most obvious result would be loss/reduction of thrust if not engine fire.
  • Impact with wing and/or flight control surfaces: Depending on the extent of the damage, an impact with the wing could cause a chunk of it falling apart, or debris damaging some of the control surfaces, with consequent reduction of lift generated by the wing, instability and/or inability to move the control surface (imagine drone parts being stuck between ailerons, flaps, etc.)
  • Front impact/cockpit incursion: Debris could damage or destroy the windshield, entering the cockpit injuring or killing the pilots (once again this depends on the size of the drone and the airspeed at the time of the midair collision
  • Impact with another part of the airframe: If the drone hit other, less critical parts of the plane, it could damage sensors, antennas and other equipment that feeds the flight data computer, resulting in a lack of information to the aircrew.
  • Distraction: If you see a drone coming close to your plane you'll probably switch your attention towards it with a consequent loss of situational awareness. This can be dangerous, especially if it happens at very low altitude, at night, in poor weather.
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A part of a drone decapitating a pilot presents obvious hazards to the flight, but the rest are more dangerous what if scenarios. Pilots are trained, exhaustively, to prepare for the unexpected, but dealing with frozen controls or dead engine puts enormous pressure on the human factor keeping that plane aloft. You're not just facing a mechanical crisis with a drone collision: you're facing a psychological one.

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I spoke with military Aircraft Maintenance Analyst Scott Triplett, who echoed that terror of the unexpected and airborne:

It's a numbers game and a play on unforeseen circumstances. Any time you add more obstacles to the field—especially ones in which the stakes are so high—you increase the negative outcome.

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But don't count out the pilots or the giant machines they're strapped to:

Most commercial aircraft are classified in "performance group A". This means they have at least two engines (maybe more) and can (in theory) suffer an engine failure at ANY stage of flight without it resulting in an accident.

If an engine fails in flight the aircraft can continue to the nearest suitable airport and land safely. If the failure occurs at high altitude the aircraft will drift down to a lower altitude when it only has one operating engine, but the flight will always be planned accordingly. The other interesting thing about performance A aircraft is that they can
always cope with an engine failure during take off, either by stopping in the remaining runway distance or by continuing the take off on the remaining engine(s). Which action to take depends on the speed at which the engine failure occurs.

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A plane like the one approaching JFK, preparing to land, was in the reddest of red zones when it comes to a potential drone-smash, Triplett explained:

Two of the most critical stages of flight are takeoff and landing. Any anomaly during these phases can lead to loss of
aircraft and in passenger airplanes loss of life. The reason why these two phases are so critical is the throttle variances for speed and the flight controls for stabilization constantly changing.

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Scott sees a spectrum of possible catastrophe:

The best case scenario is that if the aircraft comes into contact with a drone at cruising speed and no parts are ingested in to the engine/engines, minor to major damage is done to the fuselage, emergency landing procedures are implemented, and the plane lands safely.

Middle of the road: engine is damaged in-flight, that engine is shut down, and since the 747 has quad redundancy there are still 3 engines with which the aircraft can use to safely land (with potential damage to the airframe).

Worst case—and this would take all the bad juju out there in the universe: Drone ingested into engine. Blades from engine shoot out and destroy other engine on same wing and also cuts through fuel supply lines in the wing as
well as hydraulic supply lines. There are procedures to cut fuel supply, but hydraulic power is required to get these valves to shut. Even with a systemic failure like this, the plane could still land safely.

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So we have to mix assuming the best with assuming the worst, leaving us with an infinitude of disaster. The worst could happen, but you've got Denzel Washington at the stick, and a spectacular, life-saving landing happens. Or an unseen drone makes a relatively minor dink against a plane, and cascading pilot error downs the entire thing.

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But until traditional air travel is reconciled with the tens of thousands of drones already in the air, and the tens upon tens of thousands still to come once the FAA starts waving them in, each represents a possible, unwanted scenario, a single shred of metal that could unravel a billion bad contingencies moving at top speed.

The best could happen. The worst could happen. But pilots and the people they're carrying shouldn't have to consider anything unforeseen. Flight is complex enough without hovering obstacles moving, without warning or authorization, around our airports. We already have birds, blizzards, and loose screws to contend with—unwelcome drones pushed by invisible pilots aren't good news for anyone. Even hypothetically.

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DISCUSSION

Chris_Glasgow
Chris_Glasgow

Holy shit I finally get to use my degree in Aeronautical Engineering for something.

No.

If you're talking about a drone like the one pictured, it's going to have a hard time doing any serious damage. Really, you're talking an impact no worse than most bird strikes. It is absolutely not going to bring down an airliner. The idea of parts from one of these getting into an aileron and jamming it is just hilarious. The hydraulics behind those ailerons have to be able to deflect an aerofoil under pretty massive loads, it'll crush any drone parts stuck in there to dust, even if they did find a way in (and they almost certainly wouldn't).

It might do engine damage if one went in, but for high-bypass turbofans like those used on basically everything these days you'd be fairly unlucky to even have large parts of the drone pass into the compression stage of the engine. You're talking probable blade damage, possible damage to the compressor... and that's basically about it. You're not going to make an engine do its best impersonation of dynamite using a little drone...