VFR charts are required onboard an aircraft when:

VFR charts are essential for visual flight rules (VFR) operations because they provide the necessary information for pilots to navigate and maintain situational awareness in visual conditions. These charts display key elements including terrain features, airspace boundaries, navigational aids, and information about airports, which are vital for pilots who are flying visually.

When operating under VFR, pilots rely on these charts to avoid obstacles and ensure they are flying in appropriate airspace. The use of VFR charts ensures that pilots can effectively maintain visual separation from other traffic and navigate effectively based on visual references.

In situations like flying above 10,000 feet, traveling to a foreign airport, or conducting IFR operations, different requirements and charts apply that do not specifically necessitate VFR charts. For instance, IFR operations rely on instrument approach charts and en route charts specific to that type of flying. Thus, the requirement for VFR charts is explicitly tied to conducting operations under VFR.