Mayday: distress
Distress is “a condition of being threatened by serious and/or imminent danger and of requiring immediate assistance.” The call starts “Mayday, Mayday, Mayday,” and it “commands radio silence on the frequency in use”: everyone else stops talking.
Pan-pan: urgency
Urgency is “a condition of being concerned about safety and of requiring timely but not immediate assistance; a potential distress condition.” A sick passenger or a technical problem that needs a landing soon is a pan-pan. It’s said three times too, and it outranks everything on the frequency except a mayday.
Where the words come from
The international rules say each word of “pan pan” is “pronounced as the French word ‘panne’,” a breakdown. Mayday is commonly traced to French as well, m’aider (“help me”): a 1923 British newspaper announced “May-day” as the new voice distress signal and described it as the phonetic equivalent of the French for “help me.”
And the transponder
A crew in distress or urgency will often also set squawk 7700, which lights up an alarm on every controller’s screen.
