There have been scores of severe turbulence incidents in the past few years, including the high-profile "extreme turbulence" onboard a Singapore Airlines flight last year that led to the death of one passenger and injured more than 70 others.
Add to this several other occurrences where multiple passengers suffered injuries, many of which were serious and required hospitalization, and it's clear to see why turbulence is treated so seriously.
While the industry has developed sophisticated tools to help pilots avoid turbulence, there are occasions when it can't be fully avoided or hits entirely without warning. As such, pilots are trained to understand the impending signs of turbulence and what to do in each scenario.
Turbulence might not pose a significant threat to the structural integrity of an aircraft itself, but it's the passengers and crew inside who are at the highest risk (particularly crew).
This is why pilots are quick to switch the seatbelt sign on and order the crew to take their seats too if they suspect a bout of turbulence is ahead. But what are the signs that pilots look out for when it comes to possible turbulence?
1 Weather radar systems
The ability for pilots to know where turbulence might be present has improved dramatically with the implementation of better technology onboard aircraft over the decades.
Perhaps the single best weapon in a pilot's armory, so to speak, is the plane's weather radar system, which provides real-time information to help pilots make informed decisions about conditions ahead.
These systems work by reading precipitation levels and typically give pilots a color-coded look at conditions ahead, with orange and red indicating bad areas.
While this is an excellent way of spotting convective turbulence, it isn't effective at picking up clear-air turbulence (CAT), as CAT is not due to precipitation or storm clouds.
2 Pilot Reports (PIREPs) of Turbulence
One of the most reliable methods of tracking turbulence is through pilots themselves. When a pilot encounters a bout of turbulence, they will report it to Air Traffic Control (ATC) and provide details on it.
ATC will then relay this information to other aircraft entering the area so that they are aware of the potential for turbulence.
It's also possible for pilots to communicate with one another, which will usually be a faster way of sharing turbulence information if ATC is otherwise occupied with other duties.
3 Kelvin-Helmholtz Waves
When visibility is normal, pilots can see the clouds ahead out of the cockpit and are trained to recognize the signs of turbulence ahead. One of the dead giveaways of turbulence is clouds ahead that look similar to the crest of rolling ocean waves, also known as Kelvin-Helmholtz Waves.
The presence of such clouds indicates the presence of wind shear, meaning there are significant differences in speed at different layers of the cloud. According to Skybrary,
"Kelvin-Helmholtz waves are vertical waves in the atmosphere generated by wind shear. The wind shear is the result of stronger upper winds being separated from weaker lower winds by a stable layer between."
Kelvin-Helmholtz waves most commonly form in mountainous regions but have the potential to form elsewhere too. Pilots should generally avoid flying into such clouds or prepare for turbulence if they have to.
4 Wind speed variations
Spotting significant variations in wind speed across altitudes or distances can be a strong indicator of turbulent conditions. Winds aloft charts are one of the key ways of staying ahead of the weather and are received both before and during flights.
Doppler radar technology is another method of measuring current wind speeds ahead of the aircraft, although most aircraft don't have them onboard. However, ground-based radar systems can use the same technology and then inform pilots of possible turbulence ahead.
5 Proximity to mountains
The interplay between wind conditions and the terrain below is heightened in areas of high elevation, particularly mountains with their jagged terrain. One form of turbulence often encountered on aircraft is mountain wave turbulence, which occurs due to air flowing over the peaks of mountains.
Mountains tend to create lenticular clouds, which are lens-shaped and indicate heavy winds and turbulence in the area. As such, pilots have to be on their guard when flying in mountainous terrain due to the increased risk of turbulence. Mountain waves can be notably strong, raising the prospect of an aircraft encountering severe turbulence.
6 Weather forecasts
Before a flight leaves the ground, pilots have access to up-to-date meteorological information that will give them a decent idea of any possible inclement weather and turbulence ahead. While weather is notoriously unpredictable and, therefore, difficult to pin down accurately, forecasts can still be a useful tool for being aware of major storm fronts, areas of turbulence, and other hazards on the flight route.
This information will usually include METARs (Meteorological Aerodrome Reports), which are typically issued every hour and give updates on weather conditions, as well as any SIGMETs (Significant Meteorological Information) warning of serious weather ahead.
7 IATA Turbulence Aware
What's great about this tool is that it collects data from multiple participating aircraft and shares it, so that various planes all take part in inputting data to build a clearer turbulence picture. When a plane's sensors record turbulence, data is automatically sent to the ground and inserted into a database accessible to other participating airlines.
According to IATA, Turbulence Aware "receives the existing airline data from ground servers, performs quality control, deidentifies data, and provides the data back to airlines via a ground-to-ground system-to-system connection." The system also helps with geographical blind spots not well-covered by other turbulence tracking tools and allows airlines to make optimal routing decisions to reduce fuel burn.
8 Jet Stream Proximity
When a commercial airliner flies near a jet stream, there is a chance it can encounter clear-air turbulence due to sudden changes in wind speed and direction. CAT is a real pain for pilots as it is so difficult to spot with conventional tools, with pilots usually having to rely on other pilot reports instead. According to Skybrary,
When an aircraft is flying in the vicinity of a jet stream, pilots should put on the seatbelt sign as a precaution. This is not to say jet streams are all bad, as flying with the stream can actually give an aircraft a boost in speed and cut down on fuel consumption.
Will aviation respond to rising turbulence events?
Something of a debate is going on regarding whether or not turbulence events are rising due to climate change. As there are more frequent pockets of warmer air due to rising temperatures, the theory is that this will only increase both the frequency and severity of turbulence in the years ahead.
This is particularly true of clear air turbulence, which will become more frequent due to warmer temperatures. While the industry is getting better at dealing with turbulence, is there still room for improvement? With regards to CAT, because conventional instruments can't spot it, tools like IATA's Turbulence Aware become vital in enabling information sharing.
