As anyone who has flown on a plane in the last 15 years or so can attest to, flying can be stressful. Between intrusive TSA pat-downs, delays, and the fact that if you’re in a window or an aisle seat, it’s practically inevitable that someone will beg you to switch with him and take his middle seat, by mid-flight, many passengers are not in the best of moods. When the airplane jumps or dips slightly, and the captain turns on the "fasten seat belt" sign, how many people actually obey? And even when the light gets turned on, is a quick trip to the bathroom really dangerous?

We’ve all heard that flying is much safer than driving in a car, and while most of us would never think to get in a car without buckling up, flying seat belt-less seems much safer—after all, if a plane crashes, a seat belt most likely is not going to save you.

Why we wear seat belts on planes.

In 2012, as part of a ploy to sell standing seats on Ryanair, a European budget airline, CEO Michael O’Leary tried to downplay the importance of seat belts. O’Leary told the Daily Telegraph that handles should be sufficient for passengers and that seat belts “don’t matter.”

Yet most pilots tell another story. A redditor who identified as a pilot wrote last month that injuries do happen when passengers and flight attendants are up walking around during periods of turbulence:

At my own airline we have not injured any passengers (that I know of), but we've had many Flight Attendants hurt by turbulence. We've had fractured or broken necks, backs, legs, and feet. The feet get broken when that 200+ lb beverage cart gets lifted off the floor and lands on the poor FA's foot.

I spoke to another pilot who works for a major commercial airlines (he asked to remain anonymous due to corporate policy on speaking with the media). This pilot echoed the warning of the pilot on reddit.

“Not wearing a seat belt exposes a passenger (and his or her neighbors) to the risk that a turbulence encounter will lift them briefly out of their seat and then return them abruptly back down, possibly on an armrest, a galley cart or another passenger,” said this pilot via email. “If the passenger is up walking about, the potential for injury from falling or landing awkwardly on hard objects during a turbulence encounter is even greater. Therefore, observing and obeying the fasten seat belt sign is a key safety precaution.”

So how do pilots know when to turn on the "fasten seat belt" sign?

“I try to keep the fasten seat belt sign off when we are assured of smooth air and on during periods of turbulence or turbulence risk so that there is ‘credibility’ to the sign," the pilot said. "Unfortunately, due to the transitory nature of turbulence and the fact that it can be encountered suddenly and sometimes unexpectedly, the fasten seat belt sign often needs to stay on during periods that may appear to be smooth to passengers. This may desensitize passengers to the fasten seat belt sign and cause some passengers to be very casual about complying with the sign. One thing we highly recommend is that any time passengers are seated, they should keep their seat belt on even if the fasten seat belt sign is off.“

How pilots detect turbulence.

According to the pilot I spoke with, pilots have many tools that enable them to detect and avoid turbulence.

“First of all, the dispatchers who prepare our flight plans consult with our meteorology department and plan our flight paths along routes and at altitudes designed to avoid or minimize exposure to turbulence,” this pilot said.

“The flight plan includes remarks from the dispatcher alerting us to areas of known or forecast turbulence. During our preflight duties, pilots have a number of maps provided by our meteorology department that show various types of weather issues such as thunderstorms, frontal activity, winds aloft and areas of turbulence. We review these maps and use them to plan changes to routing and altitude if we do encounter turbulence along our flight. We also use this information to brief our flight attendants about when and where we may expect turbulence, so that they can adjust their service activities and be prepared.”

In other words, you know that Diet Coke you decide you need so badly that you summon a flight attendant even when the fasten seat belt light is on? Maybe not such a good idea. More planning goes into the timing of your in-flight service than you might have previously imagined.

Once the plane is in flight, pilots use weather radar systems to analyze areas of moisture for turbulence.

“So turbulence associated with thunderstorms is usually easy to avoid as we can detect the thunderstorm cells on radar and steer around them,” said this pilot. “The technology is constantly advancing too, and soon we are hoping to have on-board radar which will have the ability to detect clear air turbulence. Finally, one of our best sources of information about turbulence are reports relayed by air traffic controllers from other pilots flying ahead of our flight.”

The stats on flying seat belt-less.

I asked this pilot if he knew of injuries due to turbulence on flights, especially, as the reddit pilot noted, among flight attendants.

“Turbulence of some sort or another is common on flights, but thankfully the stronger versions of turbulence and injuries resulting from it are not nearly as common,” this pilot wrote. “I have been flying for a major airline for more than 20 years, and I can’t remember any flight I have been on where passengers were injured and only a few where crew members suffered any injuries from turbulence. The injuries were usually to flight attendants, who tend to be up and about more and were usually minor in nature like twisted or sprained ankles or bruises from hitting galley counters or carts.”

According to a 2013 article from Business Insider, the Deputy Assistant Administrator for Public Affairs at the Federal Aviation Administration repeated that around 58 passengers are injured annually in the United States due to not wearing seat belts when planes hit turbulence.

As for the stressfulness of traveling, this pilot said, “Air travel has become more complicated for our passengers, especially since September 11, and they have to deal with a lot of hassles just getting to the plane. So I like to think that once they get on board we should try to make the airplane be a bit of a sanctuary where at least for that portion of their travel experience they can relax and be somewhat hassle-free.”