Which signal is used to indicate a grave danger requiring immediate assistance?

The use of "MAYDAY" is an internationally recognized distress signal that indicates a life-threatening emergency requiring immediate assistance. When a pilot repeats "MAYDAY" three times, it conveys the urgency of the situation to air traffic control and other aircraft, emphasizing that immediate action is required to prevent loss of life or serious injury.

In aviation terms, the "MAYDAY" call is specifically reserved for critical emergencies such as engine failure, severe medical emergencies on board, or other situations where the aircraft is in distress. The protocol surrounding this signal ensures that it gets the attention of all listeners, leading to expedited rescue efforts and assistance.

Other signals, while they may indicate distress or urgency, do not indicate the same level of immediate danger. For instance, "PAN PAN" signifies an urgent situation but not an immediate life-threatening emergency, while the repetition of "EMERGENCY" or other phrases may not have the same universal recognition or established protocol as "MAYDAY."