mayday为什么是求救信号

{"name":"mayday\u4e3a\u4ec0\u4e48\u662f\u6c42\u6551\u4fe1\u53f7","type":"\u804c\u573a\u5267","area":"\u65e5\u672c","year":"2001","lang":"\u5fb7\u8bed","play":"\u84dd\u51494k","type1":"\u804c\u573a\u5267"}