Light to Severe: How Turbulence Is Rated

The turbulence severity scale has four steps: light, moderate, severe and extreme. In the United States the words come from a table in the FAA's Aeronautical Information Manual, which tells pilots how to classify and report what they flew through, and it defines each level by two things: what the aircraft does, and what happens inside the cabin (FAA, Aeronautical Information Manual 7-1-21, captured 2026-09-27). So when a crew says "moderate", the word has a published meaning.

The four levels, in the regulator's own words

These are the definitions from the FAA's Turbulence Reporting Criteria Table (TBL 7-1-21), verbatim (FAA AIM, captured 2026-09-27).

Light. Aircraft reaction: "Turbulence that momentarily causes slight, erratic changes in altitude and/or attitude (pitch, roll, yaw)." Inside the aircraft: "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. Aircraft reaction: "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." Inside: "Occupants feel definite strains against seat belts or shoulder straps. Unsecured objects are dislodged. Food service and walking are difficult."

Severe. Aircraft reaction: "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." Inside: "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."

Two things stand out. The cabin column is written around seat belts and food service, so a meal cart heading back to the galley lines up with the point where the table says food service becomes difficult. And the line between moderate and severe is control: at moderate the aircraft "remains in positive control at all times"; at severe it "may be momentarily out of control".

Chop is not the same as turbulence

The table splits light and moderate into two flavours. Turbulence changes the aircraft's altitude or attitude. Chop does not. Light Chop is "Turbulence that causes slight, rapid and somewhat rhythmic bumpiness without appreciable changes in altitude or attitude." Moderate Chop is "similar to Light Chop but of greater intensity. It causes rapid bumps or jolts without appreciable changes in aircraft altitude or attitude" (FAA AIM, captured 2026-09-27).

In plain terms, chop is the fast, washboard-road rattle; turbulence is the aircraft being nudged up, down or sideways. The table has no severe chop.

Occasional, intermittent, continuous

Intensity is only half a report. The same table gives three duration words, defined as fractions of the time spent in the bumpy air: "Occasional-Less than 1/3 of the time. Intermittent-1/3 to 2/3. Continuous-More than 2/3" (FAA AIM, captured 2026-09-27).

The manual's own sample report pairs the two, ending with "occasional Moderate Chop, Flight Level 330, DC8." Occasional moderate chop is a very different afternoon from continuous moderate turbulence.

Why the same air gets a different rating on a different aircraft

The scale describes what happened to a particular aircraft, not a fixed property of the air, and forecasters account for that.

NOAA's Aviation Weather Center publishes turbulence guidance in a measure called Eddy Dissipation Rate (EDR), and it lists different estimated thresholds for each weight class (Aviation Weather Center, GFA help, captured 2026-09-27). For a medium aircraft between about 7 and 136 tonnes maximum take-off weight, the examples given are the A320 and the Boeing 737, moderate starts at an EDR of 0.20 and severe at 0.44. For a heavy aircraft above about 136 tonnes, such as the A330 to A380, the 747 or the 777, moderate starts at 0.24 and severe at 0.54. For a light aircraft under about 7 tonnes, moderate starts at 0.16 and severe at 0.36.

It takes rougher air to move a heavy jet into the same category as a small one. Keep that in mind when two reports from the same stretch of sky disagree, whether the flight you are following is a long sector such as Singapore to London or a shorter one such as Newark to Santo Domingo.

What happens after a pilot reports it

The manual asks pilots to report turbulence to air traffic control "as soon as practicable", with the location, time in UTC, intensity, whether it was in or near cloud, altitude, aircraft type and duration (FAA AIM, captured 2026-09-27). Turbulence high up, "normally above 15,000 feet" (about 4,600 m) and away from cumulus cloud and thunderstorms, is reported as CAT, clear air turbulence, with the intensity in front of it.

The Aviation Weather Center's report symbols also carry in-between grades such as light-moderate and moderate-severe. At the top end, US SIGMETs, the warnings meant for all aircraft, are issued for severe or extreme turbulence, and the Center notes that "Any convective SIGMET implies severe or greater turbulence" (Aviation Weather Center, GFA help, captured 2026-09-27).

What the numbers say about who gets hurt

The FAA publishes a table of serious turbulence injuries on US airline (Part 121) flights, sourced from the National Transportation Safety Board. Across 2009 to 2024, its column totals are 40 passengers and 166 crew members (FAA, "Turbulence: Staying Safe," captured 2026-09-27). Crew are the people standing up, working the aisle, when the air changes.

The FAA's guidance for passengers is short: keep the seat belt buckled, and note that FAA regulations require it fastened "whenever the seat belt sign is illuminated during flight".

How TrackMyWings helps

TrackMyWings™ is a live flight-tracking platform in development, India-first in go-to-market. A private beta has run on Android since 2026-08-24, on the Play internal testing track, and public launch has no fixed date. At launch, the plan is a live map, trip management and a shared view for the family and friends waiting on someone's flight, so that someone waiting at Dubai International will be able to follow the same flight the traveller is on. Until then, the next time a crew mentions "occasional light chop", you will know exactly what they reported.

Questions people ask

What does moderate turbulence mean? In the FAA's table, moderate turbulence changes the aircraft's altitude or attitude, but "the aircraft remains in positive control at all times". Inside, occupants feel definite strain against their belts, and food service and walking are difficult.

What are the turbulence categories? Four intensities: light, moderate, severe and extreme. Each can be qualified by duration: occasional, intermittent or continuous.

Why might two aircraft report the same air differently? Because the scale describes the aircraft's response. The Aviation Weather Center's thresholds are higher for heavy jets than for medium or light aircraft, so the same air can be light for one and moderate for another.

Sources

• FAA, Aeronautical Information Manual, Chapter 7 Section 1, 7-1-21 "PIREPs Relating to Turbulence" and TBL 7-1-21 Turbulence Reporting Criteria Table, https://www.faa.gov/air_traffic/publications/atpubs/aim_html/chap7_section_1.html, captured 2026-09-27
• NOAA National Weather Service, Aviation Weather Center, GFA help (turbulence EDR thresholds, SIGMET criteria, PIREP symbols), https://aviationweather.gov/gfa/help/, captured 2026-09-27
• FAA, "Turbulence: Staying Safe" (serious turbulence injuries 2009 to 2024, NTSB data), https://www.faa.gov/travelers/fly_safe/turbulence, captured 2026-09-27