What it’s like to fly on the world’s most turbulent route

If you flew across British skies last month, you may have “enjoyed” a bumpy take-off or landing courtesy of Storm Éowyn. The most recent bout of winter weather to strike the country with enough severity to merit an official name – the Met Office lifted “Éowyn” from the pages of JRR Tolkien’s The Lord Of The Rings (Germany chose “Storm Gilles”) – had an impact on pilots and passengers alike before it dissipated on Jan 27. In one case, a British Airways flight from Las Vegas to Heathrow achieved a speed of 814mph on Jan 22, Atlantic tailwinds bringing it home some 45 minutes ahead of schedule, with bursts of turbulence to match.

In spite of this, passengers travelling across the UK can count themselves fortunate. Whatever the weather gods throw at us in this gloomiest corner of the calendar (Éowyn can scarcely be described as an isolated incident; it was the fifth formally recognised winter storm to harry Europe in January alone, following Storms Floriane, Felix, Gabri and Garoe), British airspace rarely witnesses turbulence on a par with the world’s worst.

For that, you need something that this country notably lacks: high mountains.

So much is apparent in the newest statistics released by Turbli. Produced by self-confessed “weather avgeek” Ignacio Gallego-Marcos – a Spanish expert in computational mechanics, now based in Sweden – this intriguing online database runs the numbers to calculate the flight routes that are most prone to turbulence. As a phenomenon, “turbulence is – to some extent – predictable”, Gallego-Marcos argues. And his figures point in one direction; not to Europe, but to the bottom of South America.

Of the 10 flight routes with the highest average turbulence in 2024, six involved either a take-off or a landing in the Chilean capital Santiago, or in the Argentinian cities of Salta or Mendoza. Those same three cities topped the table for the airports most afflicted by turbulence last year. Using the turbulence-intensity metric EDR (Eddy Dissipation Rate), Santiago bestrode the rankings, chalking up an average EDR of 23.065 (Mendoza came second with an average EDR of 22.755; Salta followed in third, at 20.407). The most turbulent flight over the last 12 months? The 121-mile hop from Mendoza to Santiago, which battled an average EDR of 24.684. You can assume that the seatbelt signs were on.

(Turbli splits its turbulence ratings into five EDR categories: Light (0-20); Moderate (20-40); Strong (40-60); Severe (60-80); Extreme (80-100). While Santiago et al sit in the “moderate” camp, Gallego-Marcos advises that “the ranking tables are yearly averages.”)

There is one obvious factor underpinning this data: The Andes. South America’s snow-capped spine is the longest continental mountain range on the planet, thrusting its summits into the clouds in an unbroken line of 5,530 miles, all the way from Colombia and Venezuela in the north of the landmass to Chile and Argentina at the base. The tallest member of the club is itself Argentinian; Aconcagua boasts an apex of 22,838ft (6,961m). But the Andean ridge maintains an average height of 13,123ft (4,000m) all the way down

In other words, it is quite the physical barrier. And while commercial aircraft obviously cross it at far higher altitudes, they are not immune to the atmospheric consequences of doing so. Especially if they are flying to Santiago, which sits so near to the Andes that its eastern horizon is defined by them, or to Mendoza, which lurks only 140 crow-flies miles from its Chilean neighbour, but crucially, on the other side of the ridge. Salta lies further north, where the Argentine province of the same name rubs against Bolivia and Paraguay, but goes about its business (winemaking, to gorgeous effect) on the range’s lower slopes.

An explanation as to why a vast wall of rock causes turbulence could make for a doctoral thesis. But the short answer is “lee waves” – the phenomenon whereby air currents are forced up and over a significant obstacle in their path. There are other ingredients to the recipe, including variations in atmospheric pressure, temperature, cloud levels, and the amount of moisture in the air – but the basic science is that wind flowing towards a series of peaks will need to find a way over them. And the higher the peaks, the higher the waves; in some cases, lee waves have been known to hit an altitude of 19 miles (30km). With this, planes passing over the top can expect to be buffeted by currents surging up from beneath, then pulled towards the ground by the down-drafts which inevitably ensue.

But then, while analysis such as this helps to explain why the plane you are strapped into at 36,000ft is now leaping and lurching, it does not soothe that ball of fear you feel in your stomach as the aircraft shudders in that swift, sickening motion. I can write this with specific experience.

In 20 years as a travel journalist, I have flown between the airspaces of Chile and Argentina on three occasions. I can remember the first, on approach to Santiago, with crystal clarity: the Andes, in all their pale winter glory, becoming visible below the wing – then, without warning, the Dreamliner reeling and rolling as if it had become a washing machine, and I was the clothing within it. It seemed – in my state of white-knuckled anxiety – as if this unsettling episode went on for hours. It was probably only a minute or two. It gave me a vivid image of what I could expect on future Andean crossings – but prior knowledge did nothing to reduce the worry on flights two and three.

Of course, the Andes are not the only mountains whose rocks and hard places affect aircraft. Of the four other flights in Turbli’s ten most turbulent of 2024, three involved the Nepalese capital Kathmandu or the Tibetan city Lhasa – lofty citadels of the Himalayas, perching at 4,600ft (1,400m) and 11,995ft (3,656m) respectively. This picture is repeated from continent to continent. Inevitably, Kathmandu-Lhasa was the most turbulent Asian flight last year (18.817 EDR), but the mountains also made waves in the USA, where the 349-mile route between Albuquerque in New Mexico and Denver in Colorado (17.751 EDR) was the shakiest service in North America.

In Africa, the crown wobbled on the head of the Durban-Johannesburg route, across the Drakensberg Mountains of South Africa (15.064 EDR). And even relatively flatter Australasia was in on the act, its data topped by the 190-mile air-route between the New Zealand cities of Christchurch and Wellington, whose flirtation with the Southern Alps made for an average EDR of 14.460.

As for Europe – all turbulent flight routes led to one mountain range. Each one of Turbli’s European top 10 for 2024 took off or landed or close to the Alps, with the airports of Zurich, Lyon, Basel, Milan and Venice all making the list, and the 186-mile Franco-Swiss dash between Nice and Geneva eclipsing all others for unsteadiness with an average EDR of 16.065. Remember this, the next time your approach to Heathrow is less than smooth…