What is the difference between Mayday and Pan-Pan?
Short answer
Mayday is distress with grave and imminent danger; Pan-Pan is urgency without immediate grave danger.
Use Mayday when life, vessel, or aircraft is in grave and imminent danger and immediate assistance is required. Use Pan-Pan for an urgent safety problem that needs help or advice but is not yet distress.
Quick check
What is the difference between Mayday and Pan-Pan?