this is what it sounds like. do you hear that? that's the electronic ping, it's not really audible, human ears can't pick it up. of course there's a catch to this. >> battery pingers may have only days or hours left. which apparently is a game-changer once that happens. if they can find something in the next 24 to 48 hours. joining us from london, alastair is here with us. >> good to have you here. a senior u.s. official tells cnn, actually, our pamela brown, that investigators have discovered that they programmed alternate routes and searched what to do in flight emergencies, and they called that curious. is it curious that a pilot, a captain, would do that, or is that just due diligence.