导读：5月1日是May Day，但换一种拼写，成为Mayday，就是国际通用的紧急求救信号。
A problem had arisen as voice radio communication slowly became more common. An equivalent to the Morse code SOS distress signal was needed. Obviously a word like “help” wasn’t a good choice for English speakers because it could be used in normal conversations where no one was in distress.
At the time Mockford was considering the request， much of the traffic he was dealing with was between Croydon and Le Bourget Airport in Paris， France. With both the French and English languages in mind， he came up with the somewhat unique word “Mayday”， the English spelling of the French pronunciation of the word “m’aider” which means “help me”.
When using Mayday in a distress call， it is traditional to repeat it three times in a row， “Mayday， Mayday， Mayday”. This is to make sure it is easily distinguishable from a message about a Mayday call and from any similar sounding phrases in noisy conditions.
In situations where a boat needs help， a distress call of “pan-pan” can be used instead. It means you need aid， but it’s not an emergency. Like Mayday， pan-pan is the English spelling of a French word， in this case “panne”， which means “broken/failure/breakdown”. Also， as with Mayday， one should state it three times： “pan-pan pan-pan pan-pan”， followed by which station（s） you are addressing and your last known location， nature of your emergency， etc.
If there is no reply to a Mayday or pan-pan call by the Coast Guard or other emergency agency， and a couple minutes have passed since the last call， some other radio source， such as another ship or plane that received the call， should repeat the Mayday call until a reply is received.
Vocabulary
equivalent adj. 相等的
distress signal n. 求救信号
unique adj. 独特的
distinguishable adj. 可辨别的