Instrument Meteorological Conditions
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 represents the regulations and restrictions a pilot must comply with when flying in weather conditions that restrict their ability to fly the plane only to 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 pass 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 all 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 where the pilot’s visibility outside the cockpit could be 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 is any airspace located 18,000ft up to and including 60,000ft mean sea level (MSL).
Some examples of flying in IMC are: flying through clouds, blinding rain, snow, fog, haze, cloud ceilings below 1000ft AGL (above ground level), or a prevailing visibility of less then 3 statue miles. The local controlling facility along with will determine whether conditions are IMC or VMC by using all available weather information.