pilot error. One of the pilots accidentally pushed the brake pedals, preventing the plane from obtaining the altitude needed to takeoff.
For years I had a serious fear of flying that I've only been able to overcome recently and even now, even the slightest turbulence has me white-knuckling it. Once, in an attempt to calm my fears, someone pointed out to me that the pilots didn't want to crash any more than I did. That made sense to me and helped a little, but it doesn't matter if it's simply human error. I'm kind of glad I didn't hear this report before my most recent flight, because we did hit a lot of turbulence while we were up there.
I guess there are just no guarantees in life. Not that I ever thought there were, but this is just a harsh reminder that it can all be over in an instant, no matter what precautions you take. When it's your time to go, it's just your time to go. But it's still heartbreaking. There were a lot of young guys on that plane who had their whole lives in front of them and were snuffed out in a second because someone who didn't want to die either accidentally pushed the wrong pedal.