When your plane feels like it's being thrown around the sky by an angry thunder god, should you be nervous? Actually, yes. But not for the reasons you might think. Let's take a look at what turbulence is, and the real reasons why it can be dangerous.
Some scientific stories are reassuring compared to the stories we get in pop culture. No, we aren't about to be struck down with ebola, no matter what Dustin Hoffman movies tell us. No, the internet can't turn us into felons, no matter what Sandra Bullock movies tell us. But that story you've heard about how an airplane has never been brought down by turbulence? Yep, that's a myth. One plane that was caught in turbulence was straight-up ripped apart. Another was downed due to turbulence from a thunderstorm. How can a few air bumps lead to disaster?
When Two Bodies of Air Meet Over Mountains
One of the main sources of turbulence is the confluence of two bodies of air moving at different speeds. This can happen anywhere, but it's particularly likely over mountains. Air from the ground climbs the mountain like a ramp, hitting the air above and swirling into eddies or blasting quickly into the atmosphere. In 1966, a Boeing 707 was brought down by this turbulence. The pilot had diverted from his planned flight path out of Tokyo to show his passengers Mount Fuji. The 140 mile per hour wind off the hill ripped the tail to pieces and the airplane crashed, killing everyone aboard.
Since then, jets have been made more resilient, and it's likely a modern plane would have survived the turbulence. Still, turbulence can be dangerous. The kind of turbulence most easily avoided - the kind created in a thunderstorm - contributed to a 2009 plane crash. When water vapor condenses into drops, it gives up a lot of its heat to the surrounding air. The air expands and rises quickly. The air that rises suddenly cools in the upper atmosphere just as suddenly.
Any plane going through a storm will experience sudden, unpredictable updrafts and downdrafts. The drafts can rise 50,000 feet into the air, so commercial airliners cannot rise above them. Fortunately, they're the most easily avoided, as flight paths are monitored for bad weather. When an Air France flight flew into turbulence due to thunderstorm activity, and then climbed to the aircraft's maximum flying altitude in order to avoid the unavoidable turbulence, it seems that the autopilot malfunctioned and disengaged suddenly. When other systems failed, the plane crashed into the ocean.
The Real Dangers
Turbulence doesn't have to crash a plane to cause damage. It's the number one cause of injury in nonfatal accidents. Turbulence causes changes in a plane's acceleration and altitude. When a plane is flying hundreds of miles per hour, only a bit of change in acceleration or altitude can mean a pretty big bump.
Between 1980 and 2009, three people were killed due to turbulence. One was a flight attendant. Two were passengers who hadn't been wearing their seatbelts. Hundreds have been hurt, some badly enough to be hospitalized. When a plane drops even slightly, people can literally bounce off the ceiling. Most of these injuries and deaths were due to what's called "clear air turbulence." It's invisible to radar, as it's just fast-moving currents of air. Being inside one isn't so bad. Being above or below one, where the fast-moving air breaks up the slow air all around it, is very tricky. One airline dropped 990 feet.
In the end, air travel is still incredibly safe. Although turbulence is scary, it was only a factor in one crash, and only brought down a plane that is, by modern standards, obsolete. Even the plane that made a 990 foot drop landed safely afterwards. For the most part, turbulence is why airline announcements recommend keeping your seatbelt on for as much of the flight as possible, and nothing more. Now, if you'll excuse me, I'll be down at the beach. Right at sea level. With my toes digging into the sand.