Plain English Meaning

A pilot who is flying by looking outside flies into cloud or weather thick enough that they can no longer see where they are going, and now have to fly using only their cockpit instruments — something they may not be trained or current to do.

Full Definition

A situation in which a pilot operating under Visual Flight Rules continues flight into weather conditions that no longer permit visual reference to the ground or horizon, and that legally require flight by reference to instruments. It is one of the most lethal categories of general aviation accident, typically resulting from continued VFR flight into deteriorating weather such as cloud, fog, heavy precipitation, or .