drift to contend with. >> erin mclaughlin live in perth, australia, thank you. let's talk about this with mary schiavo. >> and a cnn safety analyst and author of "why planes crash." good morning to both of you. first to you, mary. i'll ask you the question that christi just put to air. why do you believe this search area is growing? >> i think probably what they did is they were tong refine their data. they have algorithms they apply to where the pings are located and based on that they estimate where it could be from each ping. it could be five or so miles distance and how many miles deep and they keep refining that data. so i suspect with the absence of any more pings from my sono buoys. they have the four pings they have, doing their best to calculate where it might be in