Instrument Flight Rules (IFR)

IFR refers to the general weather conditions pilots can expect at the surface. IFR conditions for fixed wing aircraft means the minimum cloud ceiling is greater than 500 feet and less than 1,000 feet and/or visibility is greater than 1 mile and less than 3 miles. IFR conditions can be expected to last 30-45 minutes on average from the time an individual air mass thunderstorm begins.
Concept Mapping Toolkit
Insitute for Human and Machine Cognition
The University of West Florida