>> now, these efforts at sea are just part of the complicated operation. much of the search on the so-called northern arc involves vast areas of the rugged, highly populated territory. countries including pakistan and india say their radar would have picked up the missing plane if it had flown into their air space. we get more now from tom forman. >> we know from these satellite readings there's an idea there could be an arc to the south in the ocean. and this arc to the north. how could it go up this way? it could be very difficult. look at all the places it would have to fly through. radar systems are still there. people there, people taking a look. but even in tf the radar were na problem, there is this. there are a lot of people living in some of these areas that they almost certainly have to pass over on the way. beyond that, they have to pass over the himalayas. this is the biggest mountain range on the planet. hard to pass by day, virtually