What does a steady red light directed at an aircraft on the ground indicate?

A steady red light directed at an aircraft on the ground indicates that the pilot must stop. This signal is used to communicate that the aircraft should not proceed, as there may be potential hazards or obstacles ahead, such as other aircraft taking off or landing, or ground operations that could compromise safety. It serves as a crucial safety measure to ensure that aircraft remain stationary in situations where continuing to move could lead to dangerous encounters or accidents.

To enhance situational awareness, it’s important for pilots to recognize such signals and understand that they are crucial for maintaining safe operations in sometimes busy or complex airport environments. In contrast, other light signals serve different purposes, such as permitting take-off, instructing an aircraft to give way, or indicating the need to return for landing, which are not applicable in this instance.