an elt is set off by g-loading. an eperb is set off by saltwater. the two elts, one in the nose, one in the tail. >> this is elts, right, remind people. >> emergency locator transmission. they transmit. 406 is the key frequency. 1215 and 243 are no longer monitored by satellite. >> cockpit, door and fuselage. >> two in the nose and in the tail. the eperbss are in the compartment in the emergency exit. >> so there's no trace, everything would have to be perfectly not working in order for none of this -- do you understand what i'm saying? what's the likelihood of none of them to go off? >> in the absence of huge amounts of data -- >> right. >> as i've said, throughout the investigation, we've got enough information on the table to keep all the options open.