Glossary of Aviation Terms | Instrument Meteorological Conditions

Instrument Meteorological Conditions | Paramount Business Jets

Instrument Meteorological Conditions are more commonly referred to in the aviation world as "IMC." They represent weather conditions in which factors such as visibility, cloud distance, cloud ceilings, and weather phenomena cause visual conditions to drop below the minima required to operate by visual flight referencing. It is important not to confuse IMC with IFR, or instrument flight rules. IFR refers to the rules and restrictions that a pilot must follow when flying in weather conditions that limit their ability to fly the plane solely with instruments. On the other hand, IMC refers to the actual weather conditions present. When flying, a pilot can operate an aircraft under either instrument or visual flight rules. The Federal Aviation Administration (FAA) has established the minimum criteria for operation under either of these rules in the Federal Aviation Regulation (FAR) manual.

In order for a pilot to operate in IMC conditions, the FAA must license them. In order for a pilot to receive the proper license, they must pass a written exam and, depending on what part of the FARs their flight school operates under, a simulated and/or actual check ride in an aircraft. A check ride is a test administered by a licensed FAA inspector to an applicant in which the applicant demonstrates their ability to operate safely in an actual or simulated IMC environment. Along with the proper certification, a pilot must retain a regency of experience within the preceding 6 months in which they must safely perform procedures such as instrument approaches and holding maneuvers.

There are times when the pilot’s visibility outside the cockpit could be in visual meteorological conditions, yet they must still operate as if they were in IMC conditions. This is most commonly when a pilot is operating in class A airspace. Class A airspace includes all airspace from 18,000 feet to 60,000 feet above mean sea level (MSL). 

Some examples of flying in IMC are: flying through clouds, blinding rain, snow, fog, haze, cloud ceilings below 1000 ft AGL (above ground level), or a prevailing visibility of less than 3 statute miles. The local control facility will determine whether conditions are IMC or VMC by using all available weather information.