Flying during pristine mornings and tranquil sunsets are some of the most enjoyable moments as an aviator, but many times the air is not smooth and we hear pilots report chop or turbulence in their flight. They sound similar, but what’s the difference between chop and turbulence?
Chop causes bumps or jolts without an appreciable impact on altitude or attitude (pitch, roll, or raw), whereas turbulence causes bumps or jolts that do cause changes in altitude or attitude. Chop can only be reported as light or moderate, while turbulence can be light, moderate, severe, or extreme.
It’s important to understand and recognize the difference in chop and turbulence, as well as their respective intensities, so that we can make better flight planning decisions and offer more accurate pilot reports in the air.
What’s the difference between turbulence and chop?
As mentioned above, the main difference is that turbulence causes an “appreciable” change in altitude or attitude, while chop does not.
That being said, chop and turbulence can exist at varying intensities and varying frequencies, and it’s critically important to understand both.
Table 7-1-9 in the AIM defines the differences well. Here are excerpts from that table:
Turbulence Reporting Criteria Table
| Intensity | Aircraft Reaction | Reaction Inside Aircraft |
| Light | Turbulence that momentarily causes slight, erratic changes in altitude and/or attitude (pitch, roll, yaw). Report as Light Turbulence; 1orTurbulence that causes slight, rapid and somewhat rhythmic bumpiness without appreciable changes in altitude or attitude. Report as Light Chop. | Occupants may feel a slight strain against seat belts or shoulder straps. Unsecured objects may be displaced slightly. Food service may be conducted and little or no difficulty is encountered in walking. |
| Moderate | Turbulence that is similar to Light Turbulence but of greater intensity. Changes in altitude and/or attitude occur but the aircraft remains in positive control at all times. It usually causes variations in indicated airspeed. Report as Moderate Turbulence; 1orTurbulence that is similar to Light Chop but of greater intensity. It causes rapid bumps or jolts without appreciable changes in aircraft altitude or attitude. Report as Moderate Chop.1 | Occupants feel definite strains against seat belts or shoulder straps. Unsecured objects are dislodged. Food service and walking are difficult. |
| Severe | Turbulence that causes large, abrupt changes in altitude and/or attitude. It usually causes large variations in indicated airspeed. Aircraft may be momentarily out of control. Report as Severe Turbulence. 1 | Occupants are forced violently against seat belts or shoulder straps. Unsecured objects are tossed about. Food Service and walking are impossible. |
| Extreme | Turbulence in which the aircraft is violently tossed about and is practically impossible to control. It may cause structural damage. Report as Extreme Turbulence. 1 | |
| 1 High level turbulence (normally above 15,000 feet ASL) not associated with cumuliform cloudiness, including thunderstorms, should be reported as CAT (clear air turbulence) preceded by the appropriate intensity, or light or moderate chop. |
Frequency of Chop and Turbulence
The AIM also defines three different frequencies at which chop and turbulence can exist:
Occasional: Less than ⅓ of the time
Intermittent: ⅓ to ⅔ of the time
Continuous: More than ⅔ of the time
Another key difference in chop and turbulence is the forecasting capabilities available for both.
Can chop be forecasted?
You will not find forecasts for chop, but PIREPs (pilot reports) can include the declaration of the flight experiencing chop.
Chop is likely not forecasted because it is extremely present in everyday flying and does not cause an appreciable change in altitude or attitude to the flight, so its presence is not a hazard to pilots.
Turbulence on the other hand can become a flight hazard and is less common than chop, so it receives actual forecasts in various forms.
Can turbulence be forecasted?
Turbulence is forecasted through AIRMETs (Airmen’s Meteorological Information) and validated through PIREPs (pilot reports). Convective SIGMETs (Significant Meteorological Information) also indicate the presence of turbulence through convective (thunderstorm) activity.
For more reading on this topic, see our discussion on AIRMETs, SIGMETS, and PIREPs in our article on avoiding turbulence.
Use Your Experience to Forecast Turbulence
Outside of formal forecasts and pilot reports, you can use your own experience and intuition to plan for and deal with turbulence.
If enroute, listen to the radios. Often, pilots will make a quick informal report about weather including turbulence and chop but you need to be listening.
Workload permitting, ATC will also occasionally query pilots about the weather and the ride so we may be able to learn a lot just by listening.
You will also be able to get notice of a new Sigmet or HIWAS announcement that occurred after your flight briefing.
Use your flight planning training and experience.
Here are a few conditions that would probably produce some sort of turbulence, even if it was not forecast, that you should have learned in your primary education:
- Unstable atmosphere: If you have been watching the weather then you will see trends developing such as hot summer afternoon thunderstorms. These are indicative of an unstable atmosphere which means there is air moving around up there.
- Towering cloud formations: This is also a result of an unstable atmosphere along with high moisture content and uplifting air. These cloud formations can create turbulence that you may not see until you are inside or under the anvil with severity that can damage the aircraft.
- Warm and cold frontal movements: If the forecast calls for 95 degrees all week until Friday then the high forecast temps are only 72 after that, we know that a front will be moving through and, even if it doesn’t create a rain event, there will be an exchange and movement of air in the atmosphere.
- Forecasts for wind shear: Wind shear is another discussion, but like turbulence, it also involves parcels of air moving in different directions. If you find wind shear in the report, keep digging and find out about expected turbulence.
- Ground obstacles and friction: If you have light winds out of the south and you are landing an east-west runway that is surrounded by tall thick trees, you can expect some sort of turbulence on your approach as the wind moves past the tree lines.
- Convection: The heating of the earth is very inconsistent and the heat retention of different land features such as black paving, water in a lake, summer trees full of leaves and even the concrete jungle of a large city can produce alarming convective up and down drafts.
Practical Application of Chop and Turbulence
Choppy flight conditions will not pose a threat to the safety of the flight, but rather possible discomfort, if at all. Turbulence on the other hand can range from uncomfortable to possibly dangerous.
It is important that you research the current and forecasted weather conditions before each flight and take into consideration not only ceilings, visability, and convective activity, but also turbulence.
One of the best ways to do that is looking at PIREPs (pilot reports) along your route of flight. You can research this in many places, including ForeFlight, AviationWeather.gov, and more.
For example, below is a typical PIREP which has within it the description for Turbulence intensity as Light, Turbulence type as Chop and frequency as Occasional. For those lucky enough to fly at FL340 this report may not cause too much concern.
Below is another PIREP that describes Turbulence intensity as Moderate, type as Turbulence, and frequency as Continuous. For those lucky enough to fly at FL270 this report may create a significant concern.
Light and Moderate chop and turbulence might not be cause for canceling or rerouting your flight, but it does have an impact of the comfort of your flight. Choosing a different altitude could alleviate the issue as well.
Severe and Extreme turbulence should be avoided altogether as it can be a hazardous situation.
We also need to bear in mind that descriptions of “light” or “moderate” or any other PIREP Turbulence severity is specific to the aircraft making the PIREP.
In both examples above, these aircraft are large, heavy and moving very fast. So a smaller, lighter or slower aircraft may report these conditions as more severe. What may be moderate turbulence to a 737 may be very different for a 172.
Conclusion
Turbulence and chop are similar but different. Chop can only be light or moderate, and by definition will not cause appreciable changes in the aircraft’s attitude or altitude. Understanding the difference (as well as the different levels of severity and frequency) will help you in both your flight planning as well as your accuracy when making pilot reports.