If you are a nervous flyer, nothing sends the butterflies in the stomach skyward more than the lighting up of the fasten seatbelt sign. Now, a new analysis from turbli has found that airports in Switzerland offer two of the 10 most turbulent plane journeys in the world.

Most turbulent flight routes by turbli

Using data from 150.000 different air routes, turbli rated which services are the most likely to suffer from turbulence. This was done by analysing the “eddy dissipation rate” (edr) on the route, something company founder Ignacio Gallego Marcos described as the “measure of turbulence intensity at a given spot.” 

Turbulence in this case is defined as weather that is “caused by abrupt, irregular movements of air that create sharp, quick updraughts and downdraughts” that “occur in combinations and move aircraft unexpectedly.” According to reporting from UK news site The Independent, severe turbulence affects one in every 50.000 flights.

Two Swiss flight routes among the world's most turbulent

Top of the list for turbulent air travel was the 1.905-kilometre flight from Santiago de Chile to Santa Cruz in Bolivia. The flight from Almaty in Kazakhstan and Bishkek in Kyrgyzstan and the domestic flight from Langzhou to Chengdu in China rounded out the podium places.

However, in fifth place stood the (now-defunct) flight route between Milan and Geneva, while the flight from the Italian city to Zurich took 10th. Indeed, the routes between the two cities and Milan Malpensa were rated as the most turbulent in Europe. 

Why are flights to and from Switzerland so turbulent?

So why are these Swiss routes the bumpiest for passengers? According to the study, many of the routes in the top 10 had two things in common: mountains and short distances. According to aviation journalist Pascal Kümmerling, shorter flights are more susceptible to turbulence because planes do not have time to get to calmer, higher altitudes before having to make their descent to land.

For the second point, MeteoSwiss forecaster Ludwig Z'graggen told 20 Minuten that mountains are a source of turbulence for planes as they have more storms and cause so-called “mountain waves” - oscillations of air mass caused by the mountains and amplified by their steepness. For Switzerland specifically, he explained that “the Alps are located in the so-called westerly wind zone, often characterised by strong altitude winds”, making them more likely to cause turbulence. 

Shorter flights feel more turbulent than reality, expert says

However, Kümmerling also suggested that there may be a subjective factor at play: “When you fly less than an hour with jerks the majority of the time, it's normal to think that the flight is more turbulent. But it's all about proportion. If they last the same amount of time, but over a journey of several hours, the feeling that a flight is rough fades.”

For their part, SWISS spokesperson Meike Fuhlrott told 20 Minuten that they did not have a way of proving the findings, but assured that turbulence does “not present any danger, provided that the passengers and crew are restrained.” What’s more, “they are [also] not a factor leading to delays or diverted flights.”

10 most turbulent flight routes in the world

In all, here are the 10 most turbulent flight routes in the world:

1. Santiago (SCL, Chile) - Santa Cruz (VVI, Bolivia)
2. Almaty (ALA, Kazakhstan) - Bishkek (FRU, Kyrgyzstan)
3. Lanzhou (LHW, China) - Chengdu (CTU, China)
4. Chubu Centrair (NGO, Japan) - Sendai (SDJ, Japan)
5. Geneva (GVA, Switzerland) - Milan (MXP, Italy)
6. Lanzhou (LHW, China) - Xianyang (XIY, China)
7. Osaka (KIX, Japan) - Sendai (SDJ, Japan)
8. Xianyang (XIY, China) - Chengdu (CTU, China)
9. Xianyang (XIY, China) - Chongqing (CKG, China)
10. Zurich (ZRH, Switzerland) - Milan (MXP, Italy)

For more information, check out the official study.