The French approach of asking prosecutors to open a preliminary inquiry for manslaughter is the same as Australia's approach to opening a coronial investigation, or the USA way of combining coronial investigations with FAA investigations.
A coronial investigation occurs when the immediate or apparent cause of death /accident cannot readily be determined (not because sabotage or terrorism is suspected).
It is also a matter of course, the world over, in all airline crashes (albeit differently styled in different countries).
