every country who's involved in this are certainly looking at and trying to play out the many steps of what it would entail. tom, appreciate it. i want to bring in john hansman a professor of aeronautics. also back with us is jim tilmon. professor hanson, about all the theories out there about what happened, at this point which seem most plausible to you? >> well, we've got to keep everything on the table but a couple days ago everybody rejected the catastrophic failure idea and now it's pack on the table and that's credible. the original turn-back was towards the closest available airport, so that makes sense. so the initial part actually makes sense, some sort of catastrophic problem. >> when you say catastrophic, you don't mean instantaneous, you mean mechanical issues on board that the pilot had time to try to make that turn to try to find the closest airport. >> sure. yeah, some sort of progressive