To add and clarify what III Corps mentioned:

On all Airbus planes other than the older A300 and A310, computers prevent the pilot from putting the plane into a climb of more than 30 degrees where it might lose lift and stall. The maximum bank or roll allowed is 67 degrees. The plane's nose-down pitch is limited to 15 degrees. There are protections against overspeed.

And the computer won't allow the plane to make any extreme maneuvers that would exceed 2.5 times the force of gravity.

So I guess, I was wrong, you can crash an Airbus, as long as you don't go beyond its limits. However no one can disagree, that it (crashing/911) was much simpler in a Boeing, and the terrorist knew this.