Turbulence is part and parcel of the passenger experience in commercial aviation. We are all familiar with the bumps experienced when passing through clouds, and the (slightly stronger ones) we feel when skirting thunderstorms. But frequent fliers will also be aware of the unexpected bumps you might experience without warning. This is called Clear Air Turbulence (CAT).
Clear air turbulence is an atmospheric phenomenon that typically occurs at high altitudes where clear skies and more serene conditions prevail. Unlike the turbulence associated with thunderstorms and other visible weather systems, CAT is invisible and typically strikes without warning. It presents a manageable challenge that both pilots and passengers encounter during high-altitude flights.
What causes Clear Air Turbulence?
There are two types of Clear Air Turbulence, Mechanical and Thermal. Mechanical CAT is caused by the vertical shearing movement of air interrupting the smooth horizontal flow of air. Thermal CAT is caused by vertical air currents present when the atmosphere is unstable (put simply – warm air rising). Turbulence is categorized as ‘moderate’ or ‘severe’ on aviation weather charts.
Where does Clear Air Turbulence happen?
- Jet streams – jet streams are narrow, fast moving air currents found close to the Tropopause, where the troposphere becomes the stratosphere (around 36,000 feet). The temperature gradient between these two air masses generates turbulence. Whilst not all CAT is associated with jet streams, they are a notable driver of severe clear air turbulence. Any CAT is strongest on the coldest side of the jet stream where wind shear is highest.
- High terrain – mountainous terrain disturbs the horizontal flow of air, causing turbulence. The strength of the CAT will depend on the strength of the air flow and the shape and height of the terrain. These ‘ripples’ in the air flow can affect aircraft at significant vertical and horizontal distances from the high ground.
- Thunderstorms – Thunderstorms formed of large Cumulonimbus (CB) clouds can cause clear air turbulence in the vicinity of the storm. An aircraft passing horizontally within 20 nautical miles or less than 5,000 feet over the top of a Cumulonimbus cloud may encounter Clear Air Turbulence.
The effects of Clear Air Turbulence
Essentially, encountering CAT will result in sudden and unexpected movements of the aircraft. The aircraft will most likely experience changes in airspeed and attitude, as well as minor positive and negative G-forces associated with vertical movements.
Whilst almost all encounters with Clear Air Turbulence end without incident, there have been some notable accidents related to the phenomenon. A notable example of Clear Air Turbulence resulting in injury occurred in Indian Airspace in 2019, aboard Emirates flight EK449 from Auckland (AKL) to Dubai (DXB). According to Skybrary:
“On 10 July 2019 an Airbus A380 in the cruise at night at FL 400 encountered unexpectedly severe turbulence approximately 13 hours into the 17 hour flight and 27 occupants were injured as a result, one seriously. The detailed Investigation concluded that the turbulence had occurred in clear air in the vicinity of a significant area of convective turbulence and a jet stream. A series of findings were related to both better detection of turbulence risks and ways to minimize injuries if unexpectedly encountered with particular reference to the aircraft type and operator but with wider relevance.”
How do pilots and cabin crew respond to severe Clear Air Turbulence?
There are several key steps that flight crews can take to mitigate the effects of Clear Air Turbulence.
- Reduce speed – slowing the aircraft speed reduces the risk of structural damage to the airframe and lessens vibration. This can make it easier to read flight instruments. Aircraft typically have a turbulence penetration speed, referred to as ‘VTurb’.
- Seat Belt Signs – There’s a reason crews recommend you keep your seatbelts on at all times when seated. Pilots will notify the crew and switch on the signs to ensure all passengers and crew immediately are seated and to reduce the risk of injury.
- Suspend the cabin service – It goes without saying that it is not safe to serve beverages during severe turbulence.
- Inform Air Traffic Control – Pilots will typically make a Pilot report (‘PIREP) to notify air traffic of the conditions, thus helping other aircraft avoid them. The crew may also request a climb, descent or divergence to avoid the turbulence.
- Assess any injuries or damage – The crew will assess any damage to the aircraft or passengers and consider a diversion if necessary.
Pilots and cabin crew go through rigorous training on responding to severe turbulence and weather related events, and are well equipped to deal with the situation safely. Aircraft structural design has also evolved to absorb the pressures of severe turbulence to ensure a safe and successful flight. Whilst the crew is there to keep you safe, it’s always a good idea to keep your seat belt on.
Tracking turbulence on Flightradar24
Turbulence is one of many enhanced weather tracking features available on Flightradar24. Turbulence forecasts are available to users with a Business subscription. To view layers of turbulence on your map, head to ‘Weather’, and scroll down the list to select ‘Hi-Res Turbulence’. Turbulence forecasts are effective for 36 hours and active between flight level 100 (10,000 feet) up to flight level 450 (45,000 feet).
Cover photo: CC12214, JetPhotos.
![An example full flight summary response from the Flightradar24 API: { "data": [ { "fr24_id": "0987654321", "flight": "SK1415", "callsign": "SAS1415", "operated_as": "SAS", "painted_as": "SAS", "type": "A20N", "reg": "SE-DOY", "orig_icao": "ESSA", "orig_iata": "ARN", "datetime_takeoff": "2023-01-27T05:15:22", "runway_takeoff": "12R", "dest_icao": "EKCH", "dest_iata": "CPH", "dest_icao_actual": "EPWA", "dest_iata_actual": "WAW", "datetime_landed": "2023-01-27T06:15:10", "runway_landed": "27L", "flight_time": 3600, "actual_distance": 1007.74, "circle_distance": 6245, "category": "Passenger", "hex": "4A91F9", "first_seen": "2023-01-27T05:06:22", "last_seen": "2023-01-27T06:18:10", "flight_ended": "true" } ] }](https://www.flightradar24.com/blog/wp-content/uploads/2025/04/Flight-summary-API-cover-300x148.jpg)
![An example full flight summary response from the Flightradar24 API: { "data": [ { "fr24_id": "0987654321", "flight": "SK1415", "callsign": "SAS1415", "operated_as": "SAS", "painted_as": "SAS", "type": "A20N", "reg": "SE-DOY", "orig_icao": "ESSA", "orig_iata": "ARN", "datetime_takeoff": "2023-01-27T05:15:22", "runway_takeoff": "12R", "dest_icao": "EKCH", "dest_iata": "CPH", "dest_icao_actual": "EPWA", "dest_iata_actual": "WAW", "datetime_landed": "2023-01-27T06:15:10", "runway_landed": "27L", "flight_time": 3600, "actual_distance": 1007.74, "circle_distance": 6245, "category": "Passenger", "hex": "4A91F9", "first_seen": "2023-01-27T05:06:22", "last_seen": "2023-01-27T06:18:10", "flight_ended": "true" } ] }](https://www.flightradar24.com/blog/wp-content/uploads/2025/04/Flight-summary-API-cover-768x378.jpg)
