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.
