Under what conditions must Instrument Flight Rules (IFR) be used?

Using Instrument Flight Rules (IFR) is essential in situations where visual flight rules (VFR) are not practical or safe. When operating under VFR is deemed unsafe or illegal due to factors such as poor visibility, inclement weather, or insufficient cloud clearance, pilots must switch to IFR to safely navigate and manage their flight. IFR relies on instruments for navigation and control, ensuring that pilots can operate their aircraft safely even when they cannot rely on visual references outside the cockpit.

Linking this to the other options, if visual cues are clear, VFR would typically be the preferred method of operation. Operating below 10,000 feet does not automatically necessitate IFR use; VFR can be used in these altitudes as long as the weather conditions meet the VFR criteria. Similarly, the presence of a few clouds or visual cues does not inherently require IFR, as pilots may still operate under VFR in such conditions if visibility and cloud clearance are adequate.