Airports go to great - and often expensive - lengths to keep the approach to runways free of birds.
When birds hit aeroplane frames - or worse, go into engines - all sorts of things can go wrong. The US Federal Aviation Authority estimates that bird strikes have led to more than 200 deaths worldwide since 1988.
Now there's a new bird in the sky, and it might be more difficult to control.
When a boozed-up US Government employee crashed a drone into the grounds of the White House last Monday, he underlined just how easy it could be for miniature aircraft to get into places they're not meant to be - and just how reckless their pilots can be.
It's only a matter of time before some goof decides to get some aerial footage of a plane landing or taking off and puts a drone in its flightpath - and potentially inside the engine - of a big airliner.
They have the technology to remove the risk. Drone manufacturer, DJI, has since disabled all of its devices within 25km of downtown Washington DC.
We should shut them all down within 20km of any airport.