Final answer:
Flashing red lights from the tower indicate that the airport is unsafe and should not be landed on.
Therefore, the correct answer is: option a) airport unsafe, do not land.
Step-by-step explanation:
When flying in the vicinity of an aerodrome and you see flashing red lights from the tower, it means that the airport is unsafe and you should not land.
This is a signal used by air traffic control to indicate that conditions at the airport are not suitable for a safe landing, which could be due to various reasons such as equipment malfunctions, emergencies on the runway, or severe weather conditions.
Pilots should acknowledge the signal and generally divert to an alternate airport or hold as directed by air traffic control.
Additionally, air traffic controllers use light gun signals to communicate instructions to non-radio aircraft, ground vehicles, and people on the ground within the airfield perimeter. The signals are an essential means of reaching aircraft that do not have radios installed or that are experiencing a radio failure.