SEOUL — Ships rigged with underwater search gear are investigating a series of fleeting, deep-sea acoustic signals — detected about 300 nautical miles apart — that could be coming from the black box of a missing Malaysian airliner.
The signals provide a hopeful but confusing lead nearly a month after the plane’s disappearance. Officials coordinating the Australian-led search cautioned that verifying the sounds could be difficult.
Two signals were detected in close proximity Friday and Saturday by a Chinese patrol ship. In a separate area of the Indian Ocean on Sunday, an Australian ship picked up a signal, said retired Australian Air Chief Marshal Angus Houston, who is coordinating the search.
The process of verifying the noises remains difficult, and they could prove to be the latest in a string of false leads. The signals detected by the Chinese came from waters that are “incredibly deep” — nearly three miles to the bottom — and more ships are racing to the area to conduct follow-up work, Houston said.
The batteries that power the airplane’s locator beacons are estimated to have about a month of life in total, meaning the acoustic signals could die out by the time the ships arrive on the scene. Sunday was the 30th day of the search for Malaysia Airlines Flight 370.
“This is the most difficult search in human history,” Australian Prime Minister Tony Abbott told reporters Sunday during a visit to Tokyo. “We are searching for an aircraft which is at the bottom of a very deep ocean, and it is a very, very wide search area. We need to be very careful about coming to hard and fast conclusions too soon.”
The search for the passenger jet, which Malaysian officials say crashed in the Indian Ocean, has turned up a long list of mistaken and unverifiable leads, including several sightings of debris and floating objects that were later found to have no connection to the plane.
The aircraft’s presumed path was determined from signals it emitted to a satellite while still aloft.
Finding the black box would give investigators the best chance to discover clues about what happened aboard the flight, a red-eye from the Malaysian capital of Kuala Lumpur to Beijing.
The signals detected by the Chinese could provide a breakthrough, but officials have emphasized that there is no clear connection yet to the missing plane. China reported that the noises it heard were at a frequency of 37.5 kilohertz, matching those emitted by a plane’s emergency locator beacons.
According to Chinese state-run television, crew members aboard the Haixun 01, a patrol ship, heard the noises for 10 minutes Friday. They picked up the sounds again Saturday for 90 seconds, this time two nautical miles away from the original point of detection.
The sounds were detected using a relatively crude sonar device called a hydrophone.
“At the moment, the data we have does not provide a means of verification,” Houston said. “We have to do further investigation on the site itself.”
Houston said Sunday that the British navy’s HMS Echo and Australia’s Ocean Shield were heading to the area where the signals had been detected, about 1,000 miles west of the Australian city of Perth. The Echo is expected to arrive Monday after a 14-hour journey. The Ocean Shield will set off after investigating the “acoustic event” it had detected Sunday, Houston said. Australia had few details Sunday about that detection, and investigators were not sure of the frequency.
Both the Echo and the Ocean Shield are outfitted with sophisticated “pinger locators” — beak-like yellow devices that hunt for signals emitted from the jet’s cockpit voice recorder and flight-data recorder. Before Sunday, both vessels had been exploring a separate 150-mile track, working from opposite ends and converging in the middle. When searching for deep-sea signals, the vessels must move slowly, about 3.5 mph.
“Underwater, the environment is quite difficult,” Houston said. “There are lots of occasions when noises will be transmitted over long distances, depending on the temperature layers in the water and so on.”
The search for the passenger jet involves 12 aircraft and 13 ships scouring an area well off the western coast of Australia. In recent days, some officials involved in the search have raised concerns that the mystery of Flight 370 may never be fully solved.
Even if the black box is recovered, investigators might not be able to piece together what happened shortly after takeoff, when the plane lost contact with the ground and veered from its flight path. That’s because the cockpit voice recorder contains just two hours of the most recent audio, and Flight 370 stayed airborne for seven hours more after it steered off-course.