This has been an open secret for a while. Back in the early 90s, a colleague of mine told me that an older co-worker of us, who was nearing retirement, had worked for Thomson-CSF, and was overlooking some electronics equipment on the Île du Levant missile test center during these military exercises in September 1968.

And yes, he reportedly told my colleague, the Nice-Ajaccio flight had been indeed accidentally downed by a missile. Absolute secret was imposed by the authorities: De Gaulle was president and, four months after May 1968, and the overwhelming conservative majority at the National Assembly following the June elections, the military institutions had to be spared any embarasment, or even scrutiny, at any cost. This is the same "protecting the army at any cost" reasoning that led Charles Hernu, 18 years later, to acquiesce to a plan brought to him by the French Navy Pacific command, for sinking the Rainbow Warrior.