Under which conditions must a flight operate IFR rather than VFR?

• A. When weather allows VFR, IFR must be used.
• B. When weather prohibits VFR, IFR must be used.
• C. IFR is never used.
• D. IFR is used only on weekends.

Answer: (B)

IFR is required whenever visual flight is not possible. Visual flight relies on maintaining ground reference and seeing other aircraft to stay clear of hazards. When weather conditions drop below what’s needed for VFR—such as low ceilings or reduced visibility—you can’t maintain that visual reference safely, so flying by instruments becomes essential. In those conditions you file and fly under an IFR clearance, using instruments for navigation and ATC for separation. That’s why the correct idea is that weather prohibiting VFR necessitates IFR. The other scenarios don’t fit: if the weather is good for VFR, you can fly VFR; IFR isn’t used all the time or only on weekends.