Ships searching the southern Indian Ocean for Malaysia Airlines Flight 370 have now detected three possible “pings” from the plane’s black box recorders: On both Friday and Saturday, a Chinese ship picked up a signal of 37.5 kHz, the same frequency emitted by the devices. And, on Sunday, an Australian ship reported another “acoustic event” about 300 nautical miles away from those heard by China. “We are treating each of them seriously. We need to ensure before we leave any of those areas that this does not have any connection with MH370,” said retired Air Chief Marshal Angus Houston, the head of the Australian agency in charge of the search. However, he stressed that there is no confirmation that the signals belong to Flight 370: “This is an important and encouraging lead, but one which I urge you to treat carefully.” With the batteries that power the black boxes’ beacons set to expire within days, British and Australian ships fitted with sophisticated sound-detecting equipment are rushing to investigate the underwater noises.