Case III is defined by instrument meteorological conditions where ceiling and visibility are below which combination?

• A. 500 ft and 3 miles
• B. 2,000 ft and 5 miles
• C. 1,000 ft and 5 miles
• D. 1,500 ft and 3 miles

Answer: (C)

Instrument meteorological conditions come into play when you’re not able to meet the visual flight rule minimums, so pilots must rely on instruments. In this context, Case III is defined by ceiling and visibility thresholds that mark the boundary into IMC: a ceiling at or below 1,000 feet and visibility at or below 5 miles. When both of these limits are reached or exceeded (i.e., you’re at or under 1,000 ft ceiling and at or under 5 miles visibility), visual references are limited enough that IFR procedures are required rather than VFR.

Understanding why this is the right boundary helps: the ceiling tells you how tall the cloud layer is, and the visibility tells you how far you can see while maintaining visual reference to the ground. The combination of a low cloud base (1,000 ft) and restricted visibility (5 miles) reliably signals IMC, which is the scenario Case III represents. The other options either involve thresholds that aren’t the Case III boundary (either not low enough in the ceiling or not restricted enough in visibility) or describe more restrictive conditions that would fall into a different case.