NEW : Angus Houston says underwater signals remain ` a mystery ` and that the search for MH370 is still going on. Houston defends Malaysia 's response to the missing plane . `` At this point in time , it is too early to discount any of the acoustic detections . '' Inmarsat offers free global airline tracking to all 11,000 commercial passenger planes .
NEW : Angus Houston says underwater signals remain ` a mystery ` and that the search for MH370 is still going on. Houston defends Malaysia 's response to the missing plane . Inmarsat offers free global airline tracking to all 11,000 commercial passenger planes .