SYDNEY—After a month scouring vast stretches of land and ocean for Malaysia Airlines Flight 370, search crews are focusing on regaining contact with underwater signals consistent with the missing jet’s black box flight recorders that were first detected Saturday.
Like a solitary hunter stalking its prey, the Australian naval ship Ocean Shield—a hand-me-down from Norway’s oil and gas industry—continued to sweep a 7-mile strip of the southern Indian Ocean on Tuesday. It is towing a U.S. Navy device nearly 2 miles beneath the ocean surface, listening for pings from the black boxes’ emergency-locator beacons.
Though an aerial search for possible plane debris continued, authorities are increasingly of the view that the underwater search offers the best hope of pinpointing a possible crash site before the beacons stop emitting signals, if they haven’t already done so.
“This is the most positive, definitive lead we’ve had and we are pursuing it,” said Australian Defense Minister David Johnston, whose country is leading the multinational search off its remote western coast. “We are throwing everything at this difficult, complex task in at least the next several days whilst we believe these two pingers involved are still active.”
Beacons on the two flight recorders aboard the plane have an estimated battery life of about 30 days before they stop emitting signals. It has been more than that since the plane vanished on March 8 on a flight from Kuala Lumpur to Beijing with 239 people on board.
To avoid interfering with the delicate search for signals, authorities said Tuesday they are holding back on deploying any other ships or underwater vehicles to the search zone. Ocean Shield has been operating since April 4 in an area that investigators—based on radar, satellite communications and other data—believe is the most likely spot where the plane may have crashed. Choosing to deploy the Bluefin-21, a torpedo-shaped submersible drone currently strapped to the ship’s deck, would mark another switch in the search, effectively signaling an end to hopes of further signals from the black boxes.
“Until we stop the pinger search we will not deploy the submersible,” said retired Air Chief Marshal Angus Houston, who is heading the Australian search operation.
According to the U.S. Navy’s Seventh Fleet—which owns the black box detector equipment—a single pass can position the signal to within 2 miles, while with multiple passes the flight recorder beacons can be triangulated to within a couple of hundred yards.
If successful, it would provide by far the most promising lead yet on where the jet is presumed to have been lost into the ocean, far from the nearest airport, after disappearing from civilian radar as responsibility was being handed from Malaysian ground control to Vietnam.
Air Chief Marshal Houston said Tuesday that advice from the manufacturer of the missing jet’s black boxes suggested the signals detected this past weekend, which occurred at a frequency of 33.2 kHz, were credible. The locator beacons in the black boxes of Air France Flight 447, which crashed into the Atlantic Ocean in 2009, were designed to emit signals at a frequency of 34 kHz, he said.
The two-year underwater hunt for the black boxes of the Air France jet provides some sobering lessons for the investigation of Flight 370. Searchers missed the black boxes early—when a pinger sensor passed right above them but failed to pick up a signal, even though the rough location of the wreckage was known from the beginning.
Ultimately, underwater recovery teams returned to the initial search area, found both recorders and located the Flight 447 wreckage barely a few miles from the plane’s last transmission.
“This is a herculean task,” Australia’s Defense Minister David Johnston said Tuesday. “It’s over a very, very wide area. The water is extremely deep. This is day 32.”
Complicating any recovery effort, the area of ocean where the weekend signals were detected is some 2.8 miles deep. Those depths are at the absolute limit of the undersea vehicle aboard the Ocean Shield, which might mean that crews would have to use other submersibles or drop cameras to the ocean floor to investigate.
The ocean floor in the Air France crash was nearly 2.5 miles deep, with forbidding peaks and valleys. It took small robotic submarines provided by the Woods Hole Oceanographic Institution nearly 60 trips under the surface before the black boxes were discovered.
“It’s a large area for a small submersible with a very narrow field of search. And, of course, it’s literally crawling along the bottom of the ocean so it’s going to take a long, long time,” Air Chief Marshal Houston, the former head of Australia’s defense forces, said of the Flight 370 search Tuesday. “That’s why it’s so important to try and get another transmission. And we need to continue until there’s absolutely no chance that the devices are still transmitting.”