What does a flashing red ATC light signal indicate in-flight?

A flashing red ATC light signal indicates that the airport is unsafe for landing. When pilots receive this signal, it typically means that there is a hazard or obstruction on the runway or other serious conditions at the airport that would make landing dangerous. This signal serves as a critical alert to ensure the safety of the aircraft and its occupants, guiding pilots to either maintain altitude, circle the airport, or proceed to an alternate location.

In contrast, the other options represent different signals or situations. For instance, a clear to land instruction would be indicated by a steady green light, while a return for landing typically involves a different type of signal, such as a steady red light. The indication to give way or continue circling would also not be consistent with a flashing red, which explicitly denotes safety concerns rather than traffic management. Understanding these signals is crucial for pilot decision-making and ensuring the safety of all flights.