https://www.khaleejtimes.com/world/american-airlines-plane-crash-how-black-boxes-hold-vital-clues-to-air-disasters
They are mandatory on civil flights and the aim is to preserve clues from cockpit sounds and data to help prevent future accidents
american airlinesplane crashblack boxesholdvital
https://www.zawya.com/en/business/aviation/how-black-boxes-hold-vital-clues-to-air-disasters-r8pj44vr
The disappearance in 2014 of Malaysian Airlines MH370 triggered debate about whether data should be streamed instead
black boxesair disastersholdvitalclues