NEW : `` I think that 's something that we , as a world community , have to correct as soon as possible , '' Houston said . Rene Marsh says underwater signals remain `` the most promising lead '' `` Analysis on all four detections is continuing , he says . Malaysia defends Houston 's response to the missing plane . Inmarsat offers free global airline tracking to all four commercial passenger planes .
NEW : Rene Marsh says underwater signals remain `` the most promising lead '' `` Analysis on all four detections is continuing , he says . Malaysia defends Houston 's response to the missing plane . Inmarsat offers free global airline tracking to all four commercial passenger planes .