Those were the 70s and a famous French sentence resumed everything : "la raison d'etat" . You were told and educated in those days that you needed to protect the State, and the State would protect you.
If someone screwed up big in those days, evidence was removed and tainted to fit a "rosier" version exonerating the State.
Fortunately the French people are not very good at keeping secrets or go quiet for years. Justice is not always "aux ordres" and years later generally we get the truth.
For the Nantes collision in 1973 , it took 10 years , for the Caravelle near l' Ile du levant in 1978 it may still take a few more years, ( most probably waiting for a certain ex-minster to die ).
Those times are gone fortunately, and I sincerely do not think this will apply to the 447 inquiry.