Turbulence ⚡

Turbulence is officially categorized into four intensity levels based on its effect on the aircraft and occupants: Aircraft Reaction Occupant/Cabin Effect Slight, erratic changes in altitude or attitude. Slight strain against seat belts; liquids may splash. Moderate More intense changes; aircraft remains in positive control. Definite strain against belts; unsecured objects dislodge. Severe Large, abrupt changes; momentary loss of control.

Occupants forced violently against belts; walking is impossible. turbulence

Crucial because "severe" turbulence for a small Cessna might only be "light" for a large Airbus A380 . unsecured objects dislodge. Severe Large