If you have an urgent message to transmit regarding the safety of an airplane, what word do you prefix the message with?

The correct term to prefix an urgent message about the safety of an airplane is "pan-pan." This term is used in aviation and maritime communication to indicate an urgency that is not a full emergency. It alerts others that there is a situation requiring assistance, but it does not pose an immediate threat to life or safety. Using "pan-pan" communicates the need for attention from air traffic control or nearby aircraft without suggesting that the aircraft is in imminent danger.

In contrast, "mayday" is reserved for situations where there is a grave and imminent danger, and immediate assistance is required. The use of "mayday" indicates a life-threatening emergency, which is a more severe state than what "pan-pan" signifies. "Attention" does not specify the nature of the urgency and is not a standard term within the aviation safety communication lexicon. "SELCAL" refers to a system that alerts the crew of a specific aircraft that they are being called, but it does not convey urgency in the context of an emergency situation.