Sgt. Trent Wyatt looks out an observation window on Friday from aboard a Royal New Zealand air force P-3 Orion maritime search aircraft as it flies over the southern Indian Ocean. So far there's been no sign of Malaysian Airlines Flight 370. But officials are hoping that sounds detected below the surface are coming from one or both of the plane's black boxes. Richard Wainwright/Reuters/Landov hide caption

itoggle caption Richard Wainwright/Reuters/Landov

A Royal Australian Air Force AP-3C Orion flew past the Australian defense vessel Ocean Shield on Wednesday as the search for Malaysia Airlines Flight 370 continued in the southern Indian Ocean. LSIS Bradley Darvill/Australian Defense Force/AP hide caption

itoggle caption LSIS Bradley Darvill/Australian Defense Force/AP