Where did the phrase " pan pan" when declaring an emergency originate?
As with mayday (from venez m'aider, "come help me"), the urgency signal pan-pan derives from French. In French, a panne ([pan], "pahn") is a breakdown, such as a mechanical failure. In English, it is also sometimes[vague] pronounced as /pæn/ ("pan").
This article supports that history (and has many of the other emergency phrase histories as well).