The Click of a Seat Belt

Ah, the freedom of flying privately. No standing in line at TSA, no boarding pass or luggage-claim tickets, and no announcements selling airline-branded credit cards just as you’re drifting off to sleep. And except during takeoff and landings, you can spend the entire flight with your seat belt off if you want to...but do you really want to?

If you’ve spent a lot of time in the air, you know that turbulence can occur without warning. Sometimes it’s just a little ripple, and sometimes the aircraft can drop significantly. But what causes turbulence? And how can you keep yourself and your loved ones safe while still enjoying the luxury of flying privately?

It’s a Weather Thing…Usually

According to weather.gov, turbulence is “the most unpredictable of all the weather phenomena that are of significance to pilots.” And while your flight crew likely has access to turbulence-predicting weather information in the cockpit, it might not always be able to warn you when turbulence could hit.

Turbulence generally occurs when atmospheric imbalances try to return to a steady state. Perhaps thermal activity from the sun is warming the ground, causing some pockets of air to rise faster than others. Perhaps there is great variability in wind speed and direction due to a line of thunderstorms in the area. Or perhaps the airflow is impeded by buildings or mountains or disturbed from a passing airplane.

At lower altitudes (below 15,000 feet), most turbulence falls into one of four categories: mechanical, thermal, frontal, and wind shear. Some of these are highly predictable and can appear on weather charts or on cockpit radar screens. For example, mechanical turbulence occurs due to friction between fast-moving air and the ground or objects on the ground, so if the wind speed is 20 knots or higher and you’re flying over hilly or mountainous terrain, expect a bumpy ride. If the sun has been shining for a while and warm ground is causing thermal activity, expect the ride to be even bumpier. If there is a line of thunderstorms within a 20-mile radius indicating frontal activity (though this is not the only indication of frontal activity), your flight crew will likely turn on the “fasten seat belt” sign as the updrafts and downdrafts associated with thunderstorms can make the aircraft drop significantly.

Wind shear, however, can be a tougher nut to crack, though the technology for detecting it near airports has improved over the years. By definition, wind shear is a change in wind direction or speed over a specific distance; the more extreme the change over a short vertical or horizontal distance, the more severe the turbulence. Temperature inversions (where the air gets warmer as altitude increases, instead of getting colder) can create wind shear at the top of the inversion layer, which can be anywhere from just above the surface to several thousand feet up. Often, inversions occur at night when the ground surface is cooling, and hence the air immediately above the surface is cool while the air above that is still warm. Temperature inversions and the low-level wind shear they produce comprise one reason the “fasten seat belt” sign is illuminated during takeoffs and landings.

Above 15,000 feet, wind shear can be created by a jet stream—a narrow band of fast-moving air generated by a significant difference in air temperature—passing through slower-moving air masses. This is the most common cause of clear air turbulence (CAT), a phenomenon that often occurs without warning when jets are cruising at high altitudes in cloudless skies. During CAT, the aircraft may drop as much as a few hundred feet in a single jolt, with no warning whatsoever. CAT is undetectable by onboard weather radar, so it is extremely hard to avoid, though its shallow nature means that a climb or descent of as little as 2,000 feet can get the aircraft out of the turbulence.

At any altitude, vortices from passing aircraft can create wake turbulence. Like a water skier passing over the speedboat’s wake, an aircraft passing through another aircraft’s wake can produce a “bump.” Unlike the boat’s wake, which spreads outward on the water’s surface, an aircraft’s wake spreads out and falls downward, affecting aircraft passing behind and below. And while air traffic controllers may call out “caution for wake turbulence” if a larger, heavier aircraft (producing larger wakes) takes off or lands in front of a smaller aircraft, at altitude wake turbulence is extremely difficult to detect.

Often wake turbulence is just an inconvenient bump, but occasionally it can result in significant injuries, especially for occupants who are not wearing a seat belt. In 2017, the crew of a Bombardier Challenger 604 business jet lost control of the aircraft over the Arabian Sea after it passed through wake turbulence from an Airbus A380 traveling 1,000 feet above in the opposite direction. About 48 seconds and nearly 15 nautical miles after the aircraft passed each other, the Challenger began a sharp roll to the right, and crew inputs could not stop it. According to one account, the jet rolled three times while it lost 9,000 feet of altitude and flamed out one engine before the crew recovered the aircraft and diverted to the nearest airport. Four of the six passengers and the cabin attendant were standing when the incident occurred; all sustained injuries and the airframe itself was no longer airworthy.

Aircraft Are Built To Withstand Turbulence

The good news is that aircraft are built to withstand most types of turbulence. Even the aforementioned Bombardier Challenger with wake turbulence damage landed safely, though it never flew again. Turbulence also factors into your flight crew’s training, from using the onboard avionics to detect and avoid turbulence to the procedures once turbulence has beset the aircraft.

“As part of the discussion on the avionics, if the aircraft has the functionality to detect wind shear or turbulence, we cover it during ground school,” said Richard Meikle, Executive Vice President of Operations and Safety at FlightSafety International.

At FlightSafety, turbulence is also factored into the simulator training, triggered either by the weather phenomena already occurring in the scenario or as a separate focus item initiated by the instructor.

“FlightSafety’s current turbulence modeling approach is broken out into separate segments that handle different portions of the overall turbulence phenomena,” said Meikle. “These consist of modules that handle wind gusts, low-level wind shear, microburst, wake vortices, rough air turbulence, clear-air turbulence, and low-altitude terrain turbulence due to topography and buildings.”

Many of the turbulence models at FlightSafety were derived by industry experts such as NASA, FAA, Boeing, and other national research institutes based on real-life data and events and were validated for realism by comparing 3D modeling of the simulator flights with the actual data. For example, the rough-air model accurately mimics the randomly chaotic nature of this type of turbulence; when pilots encounter rough air or other types of moderate to severe turbulence, they may ask air traffic control for permission to climb or descend to another altitude to seek smoother air.

In addition to procedures for handling the aircraft during various types of turbulence, the crew also rehearses procedures for working with cabin crew (if any) and providing safety notices to passengers. FAA regulations (specifically Part 91.107 for business aircraft) put the onus on the pilot to ensure that everyone on board (including crewmembers) is provided with and uses a seat belt or safety harness during aircraft movement, takeoff, and landing. On large aircraft, the cabin attendants assist with this duty, but it’s still the pilot’s responsibility to ensure the safety of the aircraft’s occupants.

“When the crew experiences turbulence in the simulator, the instructor notes whether the pilot turned the ‘fasten seat belt’ sign on or not, and what kind of communication they simulate making to passengers and cabin crew,” said Meikle. “Ensuring passenger safety is core to a pilot’s job.”

Prevent Injury—Sit Down and Buckle Up!

A 2021 report from the National Transportation Safety Board (NTSB) shows the effectiveness of keeping your seat belt fastened. Of the 111 turbulence-related airline incidents studied, nearly 79 percent resulted in serious injury to just the unbelted flight attendant. Only one of the 123 people seriously injured during these incidents was documented as wearing a seat belt.

“No one is immune to the laws of physics, and your net worth doesn’t change that,” said Meikle. “Since clear air turbulence can happen unexpectedly, it’s a really good idea to keep standing to a minimum and fasten your seat belt whenever you’re seated in any aircraft.”

For comfort, Meikle recommends loosening the seat belt but by no more than a few inches. “The point of the seat belt is to ensure you don’t strike an immoveable object like the cabin ceiling,” Meikle said.

Securing children in an approved safety seat is also important. While FAA regulations allow children under the age of two to be held on an adult’s lap, this is more a nod to airline economics than safety. The NTSB noted that there have been incidents in which “caregivers have been unable to hold the infants securely during the turbulence encounter,” though no serious injuries to those infants were recorded during the study timeframe.

If you fly a lot, purchase a car seat approved for airplane use and let your broker or flight department know you’ll be bringing it along on the flight, so the crew is prepared to help you install it on the airplane.

Keep Fifi or Fido safe during turbulence by bringing a pet carrier or kennel, especially if it can be strapped in or fit under a seat. Consider a safety harness or restraint for larger animals.

Bottom Line—Turbulence Can Be Uncomfortable but Shouldn’t Be Scary

Turbulence is a normal occurrence on nearly every flight. Sometimes the turbulence is so slight you don’t notice it; usually, it’s an uncomfortable bumpiness, and on rare occasions it could be severe enough to cause injury. But your flight crew is trained to deal with turbulence, and you can take steps to keep yourself and your loved ones safe if unexpected turbulence occurs. All it takes is the click of a seat belt.