Which feature of the four-course radio was crucial for pilots?

The feature of the four-course radio that was crucial for pilots is its ability to mark four distinct courses for navigation. This technology provided pilots with a systematic way to determine their position and navigate effectively, especially in the era before advanced electronic navigation systems became commonplace. The four-course radio allowed pilots to receive directional signals that correlated to specific courses they could follow, enhancing their situational awareness and navigation accuracy during flight.

Navigational aids like this were particularly important for pilots flying over areas where visual references were limited. By being able to identify and follow precise courses, pilots could more reliably reach their destinations and avoid hazards, making it a significant advancement in aviation navigation at the time.

Other options do not align with the primary function of the four-course radio. For instance, the ability to convert fuel types, establish speed limits, or provide weather reporting were not central features of this particular radio system. Instead, its main contribution lay in enhancing navigational capabilities through defined courses.