Subchapter 9.5 – Weather Deviations and Route Changes

In IFR flight, you are cleared on a specific route at a specific altitude. That clearance is your authorization to operate in controlled airspace. However, weather—thunderstorms, microbursts, severe turbulence, icing—can render your cleared route unsafe. When you encounter weather on your route that is unavoidable, you must request a deviation.

There are two types of weather deviations: lateral (route) deviations and vertical (altitude) deviations.

Lateral deviation: You request a heading or track change to avoid a storm cell or weather system. ATC will vector you around the weather and then return you to your cleared route.

Vertical deviation: You request a climb or descent to avoid severe turbulence or icing. ATC will assign you a new altitude, often with a temporary heading change.