Terrorist strikes on space elevator cable?
I don't see a plane strike doing any damage to this material. Much like a bullet can't penetrate a silk cloth because the silk is too light and too strong. Carbon Nanotube fibre is 100 times stronger than silk.
This fibre can support a car with a thread that is too small to see! In those early tests, they quickly realized accidental contact with that tight thread caused horrible wounds! You could hit it with a baseball bat and cleave the bat!
A plane hitting this cable would just receive a large dent and then take the cable with it.. The plane would severely loose speed and, after about 200 meters, would spin off. This is also the reason the cable would be located mid ocean with closed air space and a defended support platform.