Which description defines inadvertent instrument meteorologic condition (IIMC)?

• A. A set of procedures for operating the aircraft in the event of a sudden loss of visibility due to unforeseen weather conditions
• B. Instrument flying rules
• C. Gyroscopic operation
• D. Attitude-based flight

Answer: (A)

Inadvertent instrument meteorological condition means you unexpectedly lose outside visual references and must transition to flying by reference to your instruments. The best description here captures that moment: a set of procedures you follow when visibility suddenly drops due to unforeseen weather, so you can maintain control, navigate, and safely manage the aircraft using the instruments until conditions improve or you regain outside references.

This focuses on the situation and the required actions, rather than just the rules of instrument flight, the devices themselves, or a general method of flying by attitude. The other ideas touch on related concepts—rules, gyroscopic instruments, or attitude-based flying—but they don’t define the inadvertent loss of visual reference and the associated procedure set you must follow.