Excerpted from Kim Stanley Robinson's Ministry for the Future:

So it was not really a surprise when a day came that sixty passenger jets crashed in a matter of hours. All over the world, flights of all kinds, although when the analyses were done it became clear that a disproportionate number of these flights had been private or business jets, and the commercial flights that had gone down had been mostly occupied by business travelers. But people, innocent people, flying for all kinds of reasons: all dead. About seven thousand people died that day, ordinary civilians going about their lives.

Later it was shown that clouds of small drones had been directed into the flight paths of the planes involved, fouling their engines. The drones had mostly been destroyed, and their manufacturers and fliers have never been conclusively tracked. Quite a few terrorist groups took credit for the action in the immediate aftermath, and demanded various things, but it has never been clear that any of them really had anything to do with it. That multiple groups would claim responsibility for such a crime just added to the horror felt at the time. What kind of world were they in?

One message was fairly obvious: stop flying. And indeed many people stopped. Before that day, there had been half a million people in the air at any given moment. Afterward that number plummeted. Especially after a second round of crashes occurred a month later, this time bringing down twenty planes. After that commercial flights often flew empty, then were cancelled. Private jets had stopped flying. Military planes and helicopters had also been attacked, so they too curtailed their activities, and flew only if needed, as if in a war. As indeed they were.