>> acars was either switched off or it failed. we don't know which because whatever did happen, this is the crucial moment. we pretty much know that all the coms are disabled, switched off, broken, blown up. >> is an investigator looking at this, what would the determination be at least to this point of what is happening? >> at this point, i've got two different paths. one is that that aircraft was taken over and that the systems were intentionally shut down. the other side would be that there was a singular failure at a common location, and that singular mechanical failure would have done exactly the same thing. at this point in the investigation, there's no evidence one way or the other. >> but there would be piles of evidence if acars hadn't stopped transmitting. >> you'd know the air condition of the engines, the route it was taking, the altitudes it was taking. we would know exactly the state