When pilots receive an alternating red and green signal, what should they do?

When pilots receive an alternating red and green signal, it indicates that they should exercise extreme caution. This signal is used to convey that while there may be potential hazards present, the situation is not dire and aircraft are still permitted to operate in the vicinity. Thus, pilots must be vigilant and prepared for any unexpected developments while remaining aware of their surroundings.

It's crucial for pilots to understand that this signal comes in specific circumstances, reminding them to watch for other aircraft, ground vehicles, or changing weather conditions that may affect their operations. Attentiveness during such signaling ensures safety and can prevent accidents in a busy air traffic environment like that of O'Hare Airport.