I suggest possible modes of sabotage that might have been used.
1. The old "bomb-in-the-luggage-or-mail" trick.
2. The old "psychotic-suicidal-hijacker" trick.
3. Sabotage of the engines.
4. Sabotage of the hydraulic systems.
The first two are most likely, in my opinion. The others would require knowledgable mechanics to perpetrate.
