What is indicated by a flashing red light when airborne?

When airborne, a flashing red light indicates "unsafe to land." This signal typically comes from the control tower and conveys to pilots that landing is not permitted at that moment due to various possible reasons, such as obstacles on the runway, a need for emergency responses, or unsafe landing conditions.

Understanding this signal is crucial, as a pilot seeing a flashing red light must reconsider their approach strategy and may need to gain altitude, circle the airport, or prepare for a go-around. It is essential for maintaining safety and ensuring proper air traffic management. The other choices do not reflect the urgency and safety concern that the flashing red light communicates, emphasizing the necessity of responding quickly and appropriately to such warnings.