I read that a possible reason why it ran off, was "aquaplaning", a common occurance in motorsport. Basically the tyre treads get filled with trapped water, and effectively make the tyre slick, meaning it has no grip (I think thats right). They are saying that because the plane was landing in very heavy rain, it aquaplaned.
Doesn't explain why it exploded though.
Some guy said he saw lightning before the lights went out though.
Good Job everyone survived.