Plane v Drone

There is still some controversy about the threat represented by a collision between a drone and an aircraft. There have been a number of these collisions reported in the media, and although some turned out to be bird strikes, some are real done collisions. I believe the researchers investigating drone / plane collisions can tell the difference by the presence of what we shall euphemistically call “bird residue” on the aircraft. It’s not possible for a bird to hit a plane without leaving bits of itself behind. No “bird residue” means it pretty much has to be a drone that left the dent.

Now that we have accumulated a number of these collisions, surprise surprise, it turns out that nothing much happens to the plane. Now, the fact that nothing happens, and that was the expected result of a collision between an aircraft and a drone, is no reason to think that there is no cause for concern. The aviation industry has an enviable safety record, one that just keeps getting better. The accident rate for scheduled airlines has declined from 2 fatal accidents per million flights in 1996 to less than 0.4 accidents per million flights in 2016 (according to the aviation safety network). No one died in a crash of a US certificated scheduled airline flight between 2009 and 2018.

While there are many complaints, some justified, about how the FAA has regulated the UAV and Drone industries, it is clear that they understand a thing or two about safety. You don’t get to the accident rate currently enjoyed by the industry unless you really sweat the details. These aircraft are large and complex; and there’s no shortage of things that can go wrong. You have to worry, not just about the one in a thousand, but the one in a million and everything in between. Risks most of us ignore keep the FAA up at night.

While the likelihood of a fatal accident caused by a collision between an airliner and a drone is small, we cannot prove that it is zero. It’s somewhere between the one in a thousand and one in a million.

There is a school of thought that says a collision with a drone is no worse than a collision with a bird. Since there are plenty of collisions with birds we don’t need to worry about drones. However, the aviation industry does worry about birds. And birds don’t have metal bits or batteries, both of which change the risk. A burning battery lodged in the wing of an aircraft, where most aircraft keep their fuel, would not be a good situation – especially if it wasn’t noticed.

There is another school of thought that says that we don’t have to worry because the number of drone near misses reported is exaggerated, that drones are top of mind these days and so if a pilot sees anything, they’re going to call it a drone. This is almost certainly true. A drone is not going to be visible to a pilot on final approach for long enough to get a good look. However, proponents of this point of view forget that for every drone a pilot really sees there are many drones that no one noticed.

It’s hard to know what the risk is, but it’s not zero. Of course, almost all collisions between drones and planes will end in just a few scratches or a dent. In 2016 there were almost nine million scheduled passenger flights in the US. If we want to repeat another eight years without a fatal crash of a scheduled airliner, then the FAA needs to worry not just about risks where the odds are a million to one but risks where the odds are hundreds of millions to one.

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