VMC and IMC - Definitions and Explaination

Photo © Emilio Labrador

VMC and IMC are aviation terms used to describe meteorological conditions during flight. VMC stands for visual meteorological conditions and IMC stands for instrument meteorological conditions. Although these terms are often used interchangeably with the terms VFR and IFR, even among industry professionals, VMC is not the same as VFR, and IMC is not the same as IFR. 

(There are two types of VMC, actually, and this article describes the meteorological condition and not the airspeed associated with an engine failure during multi-engine flight.)

 

VMC:

The definition of VMC, according to the FAA, is: meteorological conditions expressed in terms of visibility, distance from cloud, and ceiling equal to or better than specified minima.

The terms VMC and VFR are often used interchangeably, although VMC refers to the actual weather conditions and VFR refers to the flight rules surrounding those conditions.

The prevailing visual meteorological conditions, for example, must be at least equal to what’s required for visual flight rules (VFR), but just because a flight is conducted legally under VFR conditions doesn't mean the pilot will be in VMC the entire flight, as this article explains. Losing visual references (and inadvertently entering IMC) can happen even while maintaining VFR flight. 

 

IMC:

The definition of IMC, according to the FAA, is: meteorological conditions expressed in terms of visibility, distance from cloud, and ceiling less than the minima specified for visual meteorological conditions.

Basically, IMC is defined as any meteorological condition that’s doesn’t qualify as VMC, or any weather conditions worse than VMC.

The terms IMC and IFR are often used interchangeably, although IMC refers to the actual weather conditions and IFR refers to the flight rules surrounding those conditions.

 

All flights in IMC must be conducted by an instrument-rated pilot and under an IFR flight plan. 

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