The Airbus has little by way of mechanical design problems. There does appear to be a confusion in understanding how the computerisation is controlling the aircraft when an unforeseen event happens. That confusion largely relates to adequate training of the crew - and how closely the crew do follow their training, when an emergency is upon them.
Overall, though, the reliability of the Airbus is proven, by the tens of thousands of uneventful flights carried out on a daily basis.
So the likelihood of this event being a terrorist attack is far higher than any aircraft or crew failure.
The terrorists learn from every attack they carry out. They have found out that bombs in the centre of an aircraft do not always work effectively. They have found out that the weakest part of an aircraft is in the tail region. Damage the tail region, and the aircraft falls uncontrollably.
Sharp turns at cruise or near-cruise level, possibly in the region of 90° and 360°, as mentioned by officials, indicate to me, an aircraft with a seriously damaged tail.
Terrorists rarely brag loudly and publically about their successes today, because they know that in this electronic age, it means that they will be promptly located, and will rapidly receive on their heads, a laser-guided missile from a great height, that they don't even see coming.